A grand jury heard from a potential final witness Monday in the investigation into Donald Trump as law enforcement officials accelerated security preparations in advance of a possible indictment and as fellow Republicans staked out positions in a criminal probe expected to shake up the 2024 presidential race.

The testimony from Robert Costello, a lawyer who had a falling out with the key government witness in the Trump investigation, came as the grand jury that for months has been investigating Trump over hush money paid to a porn star during his 2016 campaign appeared to be wrapping up its work.

Costello was invited to appear after saying he had information raising questions about the credibility of Michael Cohen, a key witness in the investigation who has already appeared multiple times before the grand jury. Costello's testimony was expected to give the former president an indirect opportunity to make a case that he shouldn’t face criminal charges, though there were no clear signs his appearance had changed the course of the grand jury probe.

Cohen had been available for over two hours to rebut the testimony but was not needed, his attorney said Monday.

Costello had provided Cohen, himself a lawyer, legal services several years ago. In a news conference after his grand jury appearance, he told reporters that he had come forward to provide exculpatory information about Trump and to make clear that he did not believe Cohen, who pleaded guilty to federal crimes and served time in prison, could be trusted.

“If they want to go after Donald Trump and they have solid evidence then so be it," Costello said. “But Michael Cohen is far from solid evidence.”

Responding to Costello's claims on MSNBC later Monday, Cohen said that Costello was never his lawyer and “he lacks any sense of veracity.”

The testimony came two days after Trump said he expected to face criminal charges and urged supporters to protest his possible arrest. In a series of social media posts through the weekend, the former Republican president criticized the New York investigation, directing particularly hostile rhetoric toward Manhattan District Attorney Alvin Bragg, a Democrat.

It's not clear when prosecutors might wrap up their work, but law enforcement in New York has been making physical preparations for any unrest surrounding a possible indictment. In the morning, a New York Police Department truck began dropping off portable metal barricades that could be used to block off streets or sidewalks.

Costello briefly acted as a legal adviser to Cohen after the FBI raided Cohen’s home and apartment in 2018. At the time, Cohen was being investigated for both tax evasion and for payments he helped orchestrate in 2016 to buy the silence of two women who claimed to have had sexual encounters with Trump.

For several months, it was unclear whether Cohen, a longtime lawyer and fixer for the Trump Organization who once boasted that he would “take a bullet” for his boss, would remain loyal to the president.

Cohen ultimately decided to plead guilty in connection with the payments to porn actor Stormy Daniels and model Karen McDougal, which he said were directed by Trump. Since then, he has been a vociferous Trump critic, testifying before Congress and then to the Manhattan grand jury.

Trump, who has denied having sex with either woman, has branded Cohen a liar. Costello broke with Cohen before he pleaded guilty, after it became clear he was no longer in Trump’s camp.

In the years since, Costello, a veteran New York attorney, has represented Trump allies including his former political strategist Steve Bannon and his personal lawyer Rudy Giuliani.

Even as the New York investigation pushes toward conclusion, Trump faces criminal probes in Atlanta and Washington that, taken together, pose significant legal peril and carry the prospect of upending a Republican presidential race in which Trump remains a leading contender. Some of his likely opponents have tried to strike a balance between condemning a potential prosecution as politically motivated while avoiding condoning the conduct at issue.

Florida Gov. Ron DeSantis, an expected GOP presidential candidate, criticized the investigation but also threw one of his first jabs at the former president in a move likely to intensify their simmering political rivalry.

“I don’t know what goes into paying hush money to a porn star to secure silence over some kind of alleged affair," DeSantis said at a news conference in Panama City. “I can’t speak to that.”

But, he added, “what I can speak to is that if you have a prosecutor who is ignoring crimes happening every single day in his jurisdiction and he chooses to go back many, many years ago to try to use something about porn star hush money payments, that’s an example of pursuing a political agenda and weaponizing the office. And I think that’s fundamentally wrong.”

Mike Pence, the former vice president who’s expected to challenge Trump for the Republican nomination, castigated Trump in an ABC News interview last weekend as “reckless” for his actions on Jan. 6 and said history would hold him accountable. Even so, he echoed the former president’s rhetoric that an indictment would be a “politically charged prosecution.”

“I have no doubt that President Trump knows how to take care of himself," Pence said. “And he will. But that doesn’t make it right to have a politically charged prosecution of a former president.”