Lawyers representing Hunter Biden said Sunday that they do not expect any new evidence to turn up in the case against him just because a special counsel has been appointed to oversee the investigation and possible prosecution of the president’s son.

In an appearance on CBS’s “Face the Nation,” Abbe Lowell said the unexpected collapse of a plea agreement last month does not mean that a trial is “inevitable” and proposed three theories to explain the last-minute change of heart by prosecutors in Delaware who have been investigating the younger Biden for tax evasion, improper business dealings, and other allegations for nearly five years now.

“One, they wrote something and weren’t clear what they meant; two, they knew what they meant and misstated it to counsel; or, third, they changed their view as they were standing in court in Delaware,” Mr. Lowell said.

“One of the possibilities is the prosecutor stood up and decided for lots of reasons that might be apparent to the viewer — they didn’t like what people were saying about the deal they approved,” he added.

Mr. Lowell said he also believes that no new evidence will turn up in the case that will change the nature of the charges. If the findings by David Weiss, the Trump-appointed U.S. Attorney who now carries a special prosecutor badge, Mr. Lowell suggested, it will be because of political pressure from Republicans.

“If anything changes from his conclusion — which was two tax misdemeanors and a diverted gun charge — the question should be asked, ‘What infected the process that was not the facts in the law?’” Mr. Lowell said.

Democratic lawmakers, meanwhile, are increasingly distancing themselves and the party from Hunter Biden but clinging to the notion that President Biden remains unscathed by the growing furor and is likely to remain so.

A Democrat on the House Oversight Committee that has been so aggressively pursuing the president’s son’s case, Jaime Raskin, said in an appearance on ABC’s “The Week” that Hunter Biden “did a lot of really unlawful and wrong things” but that it is up to the justice system to determine his legal liability.

“This is why we have a Justice Department. Let’s just let them do their job,” Mr. Raskin said.

Another Democrat on the Oversight Committee, Dan Goldman, was less forthright in his comments about Hunter Biden, but admitted that the recent testimony from a new witness in the case, Hunter Biden’s former business partner, Devon Archer, does not look good for the younger Biden.

In an appearance on CNN’s “State of the Union,” Mr. Goldman repeated the White House talking point that it was the “illusion” of access to his father that Hunter Biden was selling to foreign clients and not an actual ability to affect policy.

“That’s Hunter Biden,” Mr. Goldman said. “And you can make whatever judgment you want to make about whether that was appropriate or not.”

Mr. Goldman also stressed the different reaction from Republican insiders to the indictments looming over President Trump compared to the Democratic response to the charges against Hunter Biden.

“If Hunter Biden has committed crimes, he should be charged with them. I’m a Democrat saying that,” Mr. Goldman said. “You don’t hear any currently elected Republicans saying that if Donald Trump committed crimes, he should be charged. That’s a critical distinction that the public needs to understand.”