"The option to use active duty forces in a law enforcement role should only be used as a matter of last resort, and only in the most urgent and dire of situations. We are not in one of those situations now. I do not support invoking the Insurrection Act," he told reporters. Esper also distanced himself from a maligned photo-op outside St. John's Church.
Wednesday's press briefing by Esper went over poorly at the White House, where his standing was already viewed to be tenuous, multiple people familiar with the matter said.
White House Press Secretary Kayleigh McEnany would not directly answer Wednesday whether Trump still has confidence in Esper, saying instead, "as of right now Secretary Esper is still Secretary Esper."
"With regard to whether the President has confidence, I would say if he loses confidence in Secretary Esper, I'm sure you all will be the first to know," McEnany said during Wednesday's press briefing.
"Should the President lose faith, we will all learn about that in the future," she added.
Late Wednesday night, three sources told CNN that Esper will stay on the job for now. He was at the White House for a little under three hours earlier, where he had several meetings, including one in the Oval Office with Trump.
A senior Republican source told CNN that there has been ongoing tension involving Esper and that Trump has no respect for his defense chief. Esper has had little influence and essentially takes his lead from Secretary of State Mike Pompeo, the source said, adding that this latest press conference will undoubtedly make things worse.
Trump and other top officials, including national security adviser Robert O'Brien, are "not happy" with Esper after his Wednesday remarks, three people familiar with the White House's thinking said.
One White House official said aides there did not get a heads up about the content of Esper's remarks, most notably Esper's decision to publicly break with the President on the use of the military to address unrest in US cities.
As tear gas wafted through the air in Lafayette Park across from the White House, Trump announced from the Rose Garden that if state or city leaders refuse "to take the actions that are necessary to defend the life and property of their residents," he will invoke the Insurrection Act, an 1807 law that allows a president to deploy the US military to suppress civil disorder.
Esper and Gen. Mark Milley, chairman of the Joint Chiefs of Staff, have faced a flurry of questions and criticism in the wake of Trump's comments, pressure that culminated in Esper's appearance in the Pentagon briefing room Wednesday where he attempted to distance himself from the President's rhetoric and clean up some of his own.
Asked about his use of the word "battlespace" when discussing quelling violence on the streets amid civil unrest, Esper attempted to explain that it was "something we use day in and day out ... it's part of our military lexicon that I grew up with ... it's not a phrase focused on people."
"In retrospect I would have used different wording," Esper said.
Esper also addressed the killing of Floyd, calling it a "horrible crime" and said "racism is real in America, and we must all do our very best to recognize it, to confront it, and to eradicate it."
"The officers on the scene that day should be held accountable for his murder. It is a tragedy that we have seen repeat itself too many times. With great sympathy, I want to extend the deepest of condolences to the family and friends of George Floyd from me and the Department. Racism is real in America, and we must all do our very best to recognize it, to confront it, and to eradicate it," he said.
"We are witnessing the consequences of three years of this deliberate effort. We are witnessing the consequences of three years without mature leadership. We can unite without him, drawing on the strengths inherent in our civil society," Mattis said in a statement.
"This will not be easy, as the past few days have shown, but we owe it to our fellow citizens; to past generations that bled to defend our promise; and to our children," he said.
Mattis had avoided attacking the President in his public remarks since resigning in December 2018, claiming he owes the Trump administration a "duty of silence."
Prior to his statement Wednesday, the retired four-star Marine Corps general had not mentioned Trump by name, but did implicitly criticize his former commander in chief, with whom he sharply disagreed on matters of international engagement and alliances, in a string of recent public statements and interviews.
Mattis made clear Wednesday he no longer feels bound by that same duty, issuing a scathing rebuke of the President he once served.
"Never did I dream that troops taking that same oath would be ordered under any circumstance to violate the Constitutional rights of their fellow citizensmuch less to provide a bizarre photo op for the elected commander-in-chief, with military leadership standing alongside," he said.
"We must reject any thinking of our cities as a 'battlespace' that our uniformed military is called upon to 'dominate.' At home, we should use our military only when requested to do so, on very rare occasions, by state governors. Militarizing our response, as we witnessed in Washington, D.C., sets up a conflicta false conflict between the military and civilian society," Mattis added. "It erodes the moral ground that ensures a trusted bond between men and women in uniform and the society they are sworn to protect, and of which they themselves are a part."
Meanwhile, Wednesday's events have increased the focus on the fate of Mattis' successor.
Sentiments inside the White House toward Esper had been gradually souring before this week's episode, with both Trump and O'Brien viewing Esper as not entirely committed to the President's vision for the military.
One person suggested the White House was reluctant to fire Esper given the current crisis and the fact that there are only five months left before the election. Another person suggested Trump could leave Esper in place and push blame his way. The President has a history of letting top officials languish in positions long after he's lost confidence in them.
For months, the President and O'Brien have been losing faith in Esper's ability to lead the military and his tendency to avoid offering a full-throated defense of the President or his policies, according to multiple administration officials.
O'Brien, in particular, has spoken to the President about Esper's television remarks, which the White House has viewed on repeated occasions as problematic or off-message. On at least one occasion, O'Brien presented the President with print-outs that compare his own public remarks on a topic to those of Esper to highlight the contrast.
Trump has privately expressed frustrations with Esper in recent weeks, which aides believe would likely be accelerated by his comments about the ongoing nationwide protests. He vented about Esper at length during a recent weekend at Camp David, according to multiple sources.
Those complaints have raised questions about Esper's future at the Pentagon should Trump win a second term, but his comments from the Pentagon briefing room Wednesday have prompted speculation that the timing of his departure could be moved up, the source said.
"I think this is the end for him," they added.
A US official close to Esper and familiar with White House thinking said the secretary is being "skewered" by those inside the White House for coming out Wednesday to express his views.
"(I'm) not sure who thought that was a good idea," another official told CNN.
In December, Esper sat for an interview with Fox News' Bret Baier at the Ronald Reagan Defense Forum and when asked what it was like to work for Trump, he responded, "he is just another one of many bosses I've had and you've had your time that you learn to work with."
The remark irritated the President, who tends to expect lavish praise from his Cabinet, according to two administration officials. O'Brien, by contrast, almost never breaks with the President in his public remarks. O'Brien, who took over as national security adviser last September, is said by multiple administration officials to have expressed some level of interest in the job of either secretary of state or secretary of defense, should either of those positions become available.
In the hour after his press conference ended, Esper was seen arriving at the White House alongside Milley and Attorney General Bill Barr.
The trio stood together, all wearing masks, for a few moments before entering the building.
Outside the GOP lunch Wednesday, Republican Sen. Mitt Romney said that he hopes the President will listen to Esper's perspective, telling reporters: "I think Secretary Esper has the right to express his point of view, and the President does his, and I hope the President is willing to listen to the perspective of others and take that into account as he makes his decisions."
Sen. Shelley Moore Capito, a Republican from West Virginia, said she is "glad" Esper "made his views" on the Insurrection Act known.
The secretary of defense "needs to be able to express his opinion, which is what he did," she told reporters Wednesday.
Asked whether Esper's job could be in jeopardy following his remarks, or face some backlash from the Trump, Capito said, "I would hope not," adding that the he is "expressing his opinion" and the President has to take "into consideration" that he's the leader of the US armed forces.
Asked if he still has confidence in Esper as Defense Secretary, Rep. Mac Thornberry, the top Republican on the House Armed Services simply answered: "yes."
On Tuesday, Thornberry said it would be appropriate for Esper and chairman of the Joint Chiefs, Gen. Mark Milley, to testify before the committee if the President followed through on his threat to invoke the Insurrection Act, a move that Esper made clear on Wednesday he did not believe was necessary at this time.
"I am concerned that in the current environment, it would be all too easy to put our men and women in uniform in the middle of a domestic political and cultural crisis. Discussions regarding the Insurrection Act could easily make them political pawns. The respect, trust, and support our troops have earned from their fellow citizens is the foundation of their strength and we must be careful not to erode that strength," he said in a statement.
Asked Tuesday if he had confidence in Esper, the Democratic chairman of the House Armed Services Committee, Rep. Adam Smith, said he "can't really answer that question at this point" until he speaks with Esper, which he had not done yet despite requesting a conversation with him.
Smith also called on both Esper and Milley to testify before the panel in an open hearing next week and "explain this domestic engagement to the American people."
"I have serious concerns about using military forces to respond to protestors. The role of the US military in domestic US law enforcement is limited by law. It must not be used in violation of those limits and I see little evidence that President Trump understands this fundamental premise," he said.
But while Esper attempted to clarify his view on using active duty troops to rein in protesters Wednesday, Milley was notably absent during the press briefing.
When asked why he was not present, a defense official told CNN it is because Milley believes it is up to the political and civilian control to explain the current situation.
CNN's Jeremy Diamond, Jamie Gangel, Betsy Klein, Lauren Fox, Ali Zaslav and Nicole Gaouette contributed to this report.