WASHINGTON — Former special counsel Jack Smith appeared behind closed doors on Capitol Hill this week, confronting Republican lawmakers who have accused him of waging a politically motivated campaign against President Donald Trump. In testimony that carried high legal and political stakes, Mr. Smith rejected those claims outright, saying the prosecutions he brought were grounded not in partisanship but in Mr. Trump’s own conduct.

According to excerpts of his opening statement obtained by CNN, Mr. Smith told the committee that “the decision to bring charges against President Trump was mine,” adding that the factual basis for the cases “rests entirely with President Trump and his actions, as alleged in indictments returned by grand juries in two different districts.” It was the first time Mr. Smith had testified publicly — or semi-publicly — since concluding his investigations into Mr. Trump’s efforts to overturn the 2020 election and his handling of classified documents after leaving office.

The hearing, convened by a Republican-led House committee, unfolded in private, reflecting the volatile mix of law enforcement, politics and revenge that has come to define Washington in the wake of Mr. Trump’s return to power. Republicans have portrayed Mr. Smith as the tip of a Democratic spear aimed at destroying their party’s leader, while Democrats argue that the investigation followed evidence that Americans witnessed in real time on Jan. 6, 2021, and later at Mar-a-Lago.

Mr. Smith’s decision to answer questions — rather than invoke the Fifth Amendment — was notable. Several former prosecutors from his team have faced threats of criminal referrals for declining to cooperate with the committee. Legal analysts said Mr. Smith was navigating a narrow channel: refusing to answer could invite accusations of obstruction of Congress, while speaking too freely risked claims of false statements or violations of grand jury secrecy and court orders.

Republicans on the committee, led by Jim Jordan, have argued that the investigations were “political” from the start. Mr. Jordan has repeatedly said they were designed to damage Mr. Trump’s presidential prospects rather than to enforce the law. In public remarks this week, he claimed the cases were part of a broader effort to target the Republican Party itself.

Democrats counter that the investigations were slow, cautious and at times frustratingly restrained. Former officials from the Biden White House have said privately that Mr. Smith resisted political pressure and moved only when he believed the evidence was sufficient. “If asked whether to prosecute a former president based on the same facts today,” Mr. Smith told lawmakers, “I would do so regardless of whether the president was a Republican or a Democrat.”

Much of the Republican anger centers on two decisions: the search of Mar-a-Lago in 2022 and the acquisition of phone records belonging to several Republican members of Congress. On the former, Mr. Smith’s defenders note that a federal judge found probable cause and approved the warrant, particularly after surveillance footage showed aides moving boxes of documents at the former president’s direction. Disagreements inside the F.B.I. about timing, they say, are routine and do not negate the legality of the search.

On the phone records, Mr. Smith has said the targets were not lawmakers themselves but Mr. Trump’s communications during the violent attack on the Capitol, when he sought to reach allies in Congress. The records, according to people familiar with the investigation, were obtained through standard legal process.

The hearing also illuminated a broader pattern in Mr. Trump’s second term: a relentless campaign of retaliation against perceived enemies. He has openly described himself as the “retribution” his supporters were promised, and his allies have pursued investigations of former officials who challenged him. Cases involving figures like James Comey and Letitia James have faltered or collapsed, reinforcing Democratic claims that political motivation — rather than evidence — is driving those efforts.

For Mr. Smith, the irony is stark. Republicans accuse him of weaponizing the justice system, while Democrats argue that he adhered scrupulously to the rules, even at the cost of speed. The trials he brought never reached verdicts, not because courts rejected the charges, but because the calendar ran out.

As the closed-door session stretched into its third hour, little leaked beyond prepared statements and partisan talking points. But the symbolism was unmistakable. A prosecutor who built his career on institutional restraint sat across from lawmakers demanding vengeance, while the former president at the center of the storm continued to denounce him from afar.

In that sense, the testimony was less about resolving factual disputes than about competing visions of justice itself — and whether, in an era of deep polarization, the rule of law can survive being cast as just another political weapon.