Donald Trump’s former campaign manager accused lawmakers of “focusing on petty and personal politics” in a testy hearing, as he confirmed to members of Congress that the president asked him to intervene in the Russia investigation.

As the hearing came to a close on Tuesday, the House judiciary chair, Jerrold Nadler, told Corey Lewandowski, a close Trump ally, that his behavior had been “completely unacceptable”.

“It is a part of a pattern by a White House desperate not to reveal the truth,” Nadler said. “The president’s lawyers are sitting behind you right now to make sure that you do not answer us.”

As House Democrats began what they promised would be an “aggressive series” of impeachment hearings, Lewandowski followed White House orders not to discuss conversations with the president beyond what was already public in the former special counsel Robert Mueller’s report, which described possible obstructions of justice.

Lewandowski, who declared that his questioners were “focusing on petty and personal politics” during the five-hour session, was defiant amid questioning. He demanded that Democrats provide him a copy of the Mueller report, sending Democratic staff scrambling to find one. He read directly from the report and asked Democrats to read passages to him.

During a bathroom break, Lewandowski, who is considering running for the US Senate in New Hampshire, took an opportunity to tweet a link to his new Super Pac.

Trump cheered Lewandowski along as he testified, tweeting that his opening statement was “beautiful”. Meanwhile, Republicans on the panel forced a series of procedural votes, sending the hearing into disarray.

The hearing underscores what has been a central dilemma for the judiciary committee all year as it investigates, and potentially tries to impeach, Trump. Many in the Democrats’ base want them to move quickly to try to remove Trump from office. But the White House has blocked the committee’s oversight requests at almost every turn, declining to provide new documents or allow aides and associates to testify.

Lewandowski was a central figure in Mueller’s report, which described two episodes in which Trump asked Lewandowski to tell the former attorney general Jeff Sessions to curtail Mueller’s investigation, and fire Sessions if he refused to meet with Lewandowski. Lewandowski never delivered the message, instead delegating the task to the White House aide Rick Dearborn, who declined to comply, according to the report.

Pressed by a lawyer for the Democrats, Barry Berke, Lewandowski acknowledged he might have lied in a cable interview when he said he didn’t remember the president asking him to get involved with Sessions. He added: “I have no obligation to be honest with the media because they are just as dishonest as everybody else.”

Two other witnesses who were subpoenaed alongside Lewandowski, Dearborn and the former White House aide Rob Porter, did not show up, on orders from the White House, which holds that former aides are “absolutely immune” from testifying. Democrats are challenging that position in court.