House intelligence committee chairman Adam Schiff blasted former national security adviser John Bolton on Sunday, for failing to appear for testimony in the impeachment inquiry while teasing a forthcoming memoir.
Related: Not just the facts: Republicans’ top six impeachment falsehoods
Bolton “wanted to wait for a book instead of telling the American people what he knew”, Schiff told CNN’s State of the Union, drawing a contrast between Bolton and his former deputy, Fiona Hill, who appeared before the committee on Thursday.
“The obligation right now to show the courage Dr Hill did,” Schiff said. “She made the decision that this is the right thing to do. John Bolton should make the same decision.”
Bolton, who has said he had conversations with Trump and others relevant to the investigation, has resisted testifying, warning through a lawyer that he will file suit if subpoenaed for testimony.
While he said he would prefer for witnesses such as Bolton and secretary of state Mike Pompeo to answer the committee’s questions, Schiff warned that moving the impeachment process forward was “urgent”, in order to prevent Trump tampering in the 2020 election.
“There is a sense of urgency when you have a president who is threatening the integrity of our elections that we need to act now,” he said. “If there is not deterrent … we can darn well be sure this president will commit even more egregious acts in the months ahead.”
If there is not deterrent … we can darn well be sure this president will commit even more egregious acts
Schiff said the impeachment investigation was ongoing and “we have continued to learn more information every day”, but added that “the evidence is already overwhelming” and said he hoped Republicans would rise to what he called a “constitutional duty” to consider impeachment.
The intelligence committee is working on a report it is expected to submit to the judiciary committee in early December, although the report could have “addenda”, Schiff said. “We don’t foreclose the possibility of more depositions or hearings,” he said. “We are in the process of getting more records.”
The judiciary committee will decide if impeachment proceeds, and on what grounds. A vote in the House could likely pass largely on party lines but conviction in the Senate seems unlikely.
The White House is preparing for a Senate trial, Trump adviser Kellyanne Conway said on CBS’s Face the Nation, but Trump’s team also has not ruled out that an impeachment vote would not be taken in the House.
“We’re preparing for both eventualities,” she said. No Republicans in the House or Senate have said they favour impeachment.
Schiff said he “would hope there would be Republicans who would be willing to step forward. It shouldn’t matter that this is a Republican president. If this had been a Democratic president, I would be among those leading the way and saying we have to” pursue impeachment.
On NBC’s Meet the Press, Schiff said: “I mean they seem to be saying, ‘Unless Donald Trump writes out ‘I bribed Ukraine’, the evidence will be insufficient.
“Are we prepared to say that soliciting foreign interference, conditioning official acts … to get political favors is somehow now compatible with the office?” he asked.
They seem to be saying, ‘Unless Donald Trump writes out ‘I bribed Ukraine’, the evidence will be insufficient
On Sunday afternoon, the Washington Post cited three anonymous sources in reporting that an internal White House review had uncovered “extensive efforts to generate an after-the-fact justification” for the decision to withhold aid, efforts involving acting chief of staff Mick Mulvaney which “could at a minimum embarrass the president”, causing political and even legal problems.
Mulvaney is among Trump officials who have refused to co-operate with the impeachment inquiry. Schiff continued: “Are we also prepared to say that Congress will tolerate the complete stonewalling of an impeachment hearing or process? Because if we do it will mean that the impeachment clause is a complete nullity.”
Schiff said a party-line vote on impeachment was a possibility: “I think it will mean a failure by the GOP to put the country above their party and it will have very long-term consequences if that’s where we end up.”
Hill testified that US officials were engaged on a “domestic political errand” in Ukraine, at odds with national security policy.
“It became very clear the White House meeting itself was being predicated on other issues,” she said, “namely investigations and the questions about the election interference in 2016.”
Schiff was asked about a CNN report which said his top Republican colleague on the intelligence committee, Devin Nunes, traveled last year to Austria and met with Ukrainians on a political errand targeting Joe Biden. The Democrat said the matter was for the ethics committee.
If Nunes “was traveling on taxpayer funds to dig up dirt on Biden, that will be an ethics matter, that’s not before our committee”, Schiff said.
Nunes has denied wrongdoing and threatened to sue CNN and the Daily Beast, which also reported the story.
Over the weekend, Republicans continued to ignore a warning issued by Hill not to advance the “fictional narrative” of Ukrainian election hacking, which “has been perpetrated and propagated by the Russian security services themselves.”
Related: Trump impeachment: Giuliani plays down Parnas link and repeats ‘insurance’ claim
Trump has taken lead in advancing the narrative, out of an apparent desire to rewrite the history of Russian tampering meant to boost his 2016 campaign.
Louisiana senator John Kennedy told Fox News Sunday it was impossible to know who was behind the 2016 hacking of the Democratic National Committee and Hillary Clinton’s campaign.
“I don’t know,” Kennedy said. “Nor do you. Nor do any of us.”
The US intelligence community has unanimously concluded that Russia was behind the election tampering, which has been forensically traced to an operations center inside Russia, whose Russian funding and ultimate direction by President Vladimir Putin has been documented.