The political isolation of Jack Evans, the District’s longest-serving elected official, has never been greater.

Evans (D), who has represented Ward 2 on the D.C. Council for 28 years, had been largely successful in deflecting politicians’ concerns about his ties to lobbyists and developers — questions at the center of an ongoing criminal investigation and multiple government ethics probes.

But his defenses have crumbled in recent weeks, as the findings of an ethics investigation commissioned by the Metro board became public and FBI agents stepped up pressure on the council member with a dawn search of his Georgetown home.

Now council colleagues who in the past have either defended Evans or refrained from attacking him are abandoning him. On Friday, D.C. Mayor Muriel E. Bowser (D) — who counts Evans as one of her strongest allies at city hall and has pointedly refrained from commenting on his problems — called on him to step down as chairman of the council’s powerful finance committee, as lawmakers launch an investigation into Evans’s alleged conflicts of interest.

Some campaign donors who have fueled his seeming invincibility at the ballot box say Evans, 65, can no longer count on their support. He faces multiple challengers in his reelection effort next year, as well as a recall campaign.

“He’s on a very slippery slope. In the short term, I don’t see any solutions,” said Ron Lester, a pollster whose clients have included council member and former mayor Vincent C. Gray (D-Ward 7) and former mayor Marion Barry.

Evans’s long-standing relationships in Washington’s business community give him “institutional support that shouldn’t be discounted,” Lester added. “But in the court of public opinion, that’s not going to help him.”

Evans did not return calls for comment.

A skilled retail politician, Evans has always counted on his ability to navigate controversy. And when scandal started brewing 18 months ago, it initially seemed he would be able to do so again.

But the extent to which Evans’s fortunes have changed came into focus Tuesday at a D.C. Council session at which he tried — by all appearances, without success — to persuade fellow lawmakers not to strip him of his prized committee chairmanship and not to launch an investigation into his conduct.

Council member Elissa Silverman (I-At Large) said the question-and-answer session had gone “horribly” for Evans. “I don’t think Jack persuaded anyone,” she said.

Evans had requested the meeting to fend off allegations contained in a report produced by a law firm hired by the Metro board to perform an investigation of his conflicts of interest.

Among its findings was that Evans repeatedly used his position as the board’s chairman to benefit a consulting client that was secretly paying him $50,000 per year.

After The Washington Post published the report, Evans resigned from his position overseeing the regional transit agency.

Evans has acknowledged that he committed an ethics violation by not disclosing a conflict of interest. However, on Tuesday, he also downplayed that conflict, saying his client did not have business with Metro.

Metro launched its investigation after The Post reported that Evans, seeking employment with law firms that lobby the D.C. government, sent those firms business proposals offering his connections and influence as a council member and Metro board chairman.

Evans is also facing a city ethics investigation into whether he improperly aided a digital sign company that was locked in a battle with D.C. officials over the legality of its signs. The company’s founder gave Evans checks worth $50,000 and issued him 200,000 stock shares in the company; Evans said he returned the checks and stock.

“When all is reviewed and known, you will see my actions — while not becoming — are far from that which has been reported or suggested,” Evans said at the outset of the meeting on Tuesday.

But over the next two hours, as Evans held forth in his defense and answered — or dodged — questions from other legislators, little was added to the facts already in the public record.

As his fellow council members grilled him about the findings of the Metro investigation and other matters arising from his work on the council, Evans started to appear weary and remote, staring at a pen he twirled in his hands.

He frequently said he did not recall or was not at liberty to discuss the information requested by his colleagues, a far cry from his previous, brash dismissals of alleged misconduct. Addressing the FBI search of his house, he said that the boxes agents carried away were “almost entirely empty.”

After the meeting broke up, several lawmakers said they thought Evans, in attempting to explain himself, had lost more credibility.

“I think it’s worse now,” said Charles Allen (D-Ward 6), who became visibly frustrated during the meeting as Evans declined to answer questions about the digital sign company.

“He’s misled us before,” Allen said. “How do I trust whatever answers he’s given us today?”

In one measure of Evans’s standing with his colleagues, two of the council’s 13 members refused to attend the meeting because Evans was not placed under oath.

A majority of council members have said they will vote at their next meeting Tuesday to strip Evans of the finance committee chairmanship, and D.C. Council Chairman Phil Mendelson (D) said he plans to hire a law firm to investigate Evans and form a committee to review the findings.

In response to questions from The Post, a spokeswoman for Bowser on Friday issued a statement that echoed calls for Evans to give up his committee leadership as the council’s investigation plays out.

“Council member Evans has served the residents of Washington, D.C. for nearly three decades, and we know how dedicated he is to improving the lives of Washingtonians,” the statement read. “However, the recent allegations warrant further review. . . . It is prudent for the council to review the matter and for the council member to relinquish his chairmanship.”

Some campaign donors reached by The Post last week said they worried about Evans’s political future.

“I would not at this point give him money,” said Morton Funger, a prominent developer and reliable Evans contributor over the years. He said the council member’s political fortunes seem tenuous enough that he would not continue to support him “unless I find out that whatever they’re trying to accuse him of is not correct.”

Chris Donatelli, another developer who has contributed money to Evans’s campaigns, said he was “still standing by Jack because he has done a lot for D.C.”

But he also said he is waiting to hear Evans explain some of the facts that have emerged before he commits to supporting his future campaigns.

“I’m rooting for Jack,” Donatelli said, “but to be honest, I feel like I’m pulling for an underdog at this point.”

With Evans up for reelection in 2020, much could depend on how quickly the federal investigation advances. Five challengers have already entered the Ward 2 Democratic primary.

Lester, the pollster, said District voters’ weariness with politicians’ ethics scandals — including federal investigations that forced council members Harry Thomas Jr., Michael A. Brown and Kwame Brown from office over the past decade — has left them with a low tolerance for even the appearance of misconduct.

“You don’t have to be indicted or convicted to lose the support of most voters in D.C., because they have been through a lot,” Lester said.