WASHINGTON — Despite President Donald Trump's public declaration that he isn't concerned about impeachment, he has told people close to him in recent days that he is alarmed by the prospect, according to multiple sources.

Trump's fear about the possibility has escalated as the consequences of federal investigations involving his associates and Democratic control of the House sink in, the sources said, and his allies believe maintaining the support of establishment Republicans he bucked to win election is now critical to saving his presidency.

On Wednesday Trump was delivered another blow when federal prosecutors announced an agreement with American Media Inc, in which the publisher of the National Enquirer admitted to making a $150,000 payment in 2016 to silence a woman alleging an affair with Trump, in coordination with his presidential campaign, to prevent her story from influencing the election.

The agreement with prosecutors in the Southern District of New York follows the admission by the president's former personal lawyer, Michael Cohen, that he violated campaign finance laws by arranging hush payments to women in 2016 at the direction of Trump.

“The entire question about whether the president committed an impeachable offense now hinges on the testimony of two men: David Pecker and Allen Weisselberg, both cooperating witnesses in the SDNY investigation," a close Trump ally told NBC News.

Weisselberg is the chief financial officer for Trump organization who was allegedly in the center of the hush money operation. He was reportedly granted immunity for his testimony. Pecker is the chief executive at AMI.

The developments leave Trump as the lone party who argues the payments were not intended to influence the election.

They also come as Trump’s search for a chief of staff is in disarray, with no consensus around a single choice in sight after multiple potential candidates have signaled they're not interested in the job.

The president has yet to acquire a team to combat the expected influx of congressional investigations and continued fallout from multiple federal investigations of his associates. He’s been calling around to his friends outside the White House and allies on Capitol Hill to vent and get the input. On Wednesday the president wasn't in the Oval Office until noon.

The White House declined to comment on this report.

Yet despite his frustrations behind the scenes, Trump has tried to maintain a confident public posture.

"It's hard to impeach somebody who hasn't done anything wrong and who's created the greatest economy in the history of our country," Trump said Tuesday in an interview with Reuters. "I'm not concerned, no. I think that the people would revolt if that happened."

Some Republican lawmakers have signaled cracks in what has been a solid wall of support for Trump amid intensifying federal investigations after prosecutors said Friday that Trump directed Cohen to arrange illegal payments to two women alleging affairs.

"Am I concerned that the president might be involved in a crime? Of course," Republican Sen. Bill Cassidy of Louisiana told reporters Tuesday. "The only question is, then, whether or not this so-called hush money is a crime," he added.

Republican Sen. Marco Rubio of Florida rattled the White House with similarly cautious remarks Sunday when asked about Trump's possible involvement in the violation of campaign finance laws: "If someone has violated the law, the application of the law should be applied to them like it would to any other citizen in this country, and obviously if you're in a position of great authority like the presidency that would be the case."

Rubio said his decision on how Congress should respond to federal investigators' final findings on the payments "will not be a political decision, it'll be the fact that we are a nation of laws and no one in this country no matter who you are is above it."

Republican lawmakers, however, have largely shrugged off the latest twists in the investigations involving Trump’s close associates and have signaled their strong support for him.

The incoming chairman of the House Judiciary Committee, Democrat Jerry Nadler of New York, said that same day that the president may have committed "impeachable offenses."

Federal prosecutors in New York state in the court documents that the payments violated campaign finance laws and were arranged by Cohen "in coordination with and at the direction of" Trump.

The president has been on a days-long tirade, sources tell NBC News, lashing out at his own staff and lawmakers on Capitol Hill, frustrated by the threat of a Democratic House with subpoena power, an array of looming congressional investigations, multiple intensifying federal probes, a botched effort to find a new chief of staff and a potential partial government shutdown over a lack of funding for his top campaign promise — a border wall.

Trump has ranted about why no one around him is doing anything to stop any of it and vented about the lack of support he believes he has in Congress and within his own White House, the sources tell NBC News.

In addition to the much-anticipated report from Mueller on the Russia investigation, Democrats could ask prosecutors in the SDNY to similarly share details of their probe into Cohen that are related to the president.

Trump has in recent days been made aware of this possibility from people close to him, opening up a new vulnerability for the president.