Trump’s defense team and his Republican allies have argued against the inclusion of witnesses at impeachment trial

Republicans do not yet have the needed votes to block witnesses from appearing at the Senate impeachment trial of Donald Trump, the majority leader, Mitch McConnell, told his caucus in a meeting on Tuesday night, according to multiple reports.

With an unknown number of Republican senators still undecided on the question of calling witnesses, McConnell could still get the votes he needs to block witnesses and stop the trial from reeling off into unpredictable – and potentially hazardous – territory for the president. At least four Republicans would need to join Democrats to force witness testimony.

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Trump’s defense team and his Republican allies have argued vehemently against the inclusion of witnesses at the trial, saying they already had enough information to decide the case and that the Senate should not be burdened by what they have framed as an incomplete process in the House of Representatives.

But those arguments appear not to have been persuasive to the necessary number of senators. Trump’s lawyers concluded their opening arguments on Tuesday.

Led by Trump’s personal lawyer Jay Sekulow, the defense team dismissed objections to Trump’s conduct towards Ukraine as “policy disagreements” and warned senators not to “lower the bar of impeachment” by voting to convict the president.

The defense team briefly grappled with charges reportedly appearing in an unpublished manuscript written by the former national security adviser John Bolton that Trump had conditioned security aid for Ukraine on the delivery of personal political favors.

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Even if Trump did that, his lawyers said, it would not be impeachable. But reports about the Bolton book were in any case “inadmissible” as evidence, Sekulow argued, owing to the secondhand nature of those reports.

“You cannot impeach a president based on an unsourced allegation,” Sekulow said. “Responding to an unpublished manuscript that maybe some reporters have an idea of maybe what it says – if you want to call that evidence, I don’t know what you want to call that – I’d call that inadmissible.”

A two-thirds majority of voting senators is required to convict Trump. An acquittal, much more likely, could be voted on as early as Friday. In the final visible hurdle remaining between Trump and acquittal, senators planned to vote, also on Friday, on whether to call witnesses in the case.

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Before McConnell told his caucus that he was short on votes, Republicans had threatened to respond to witnesses called by Democrats with a call for witnesses whom Democrats say are irrelevant to the case but whom Trump has been very much focused on: former vice-president Joe Biden, his son Hunter Biden, the whistleblower whose complaint launched the impeachment inquiry and potentially others.

Hearing from numerous witnesses could extend the impeachment trial, which began last week and so far has had a brief run by historical standards, into next month and potentially beyond.

But if Sekulow’s argument sounded like a call for Bolton to testify, that was an aberration from the strong posture of the defense team against witnesses and in favor of ending the trial as quickly as possible.

The White House was reportedly spreading the word to senators on Tuesday that calling Bolton or other witnesses would result in a court battle that would prolong the trial indefinitely. Republican senators were to meet on Tuesday afternoon to discuss strategy for the next phase of the trial, a two-day question period in which queries submitted by senators in writing will be read aloud by the chief justice, John Roberts, who is presiding.

It is still far from certain that witnesses including Bolton will testify, but since Sunday night, when Bolton’s manuscript was first reported, some more moderate Republican senators have voiced openness to the prospect, a sticking point for congressional Democrats in the impeachment trial.

“Certainly a few days ago [the chance of witnesses being called] was zero and now it’s something,” Republican strategist Rob Jesmer told the Guardian. “I think that will massively prolong the trial.”

Facebook Twitter Pinterest Chuck Schumer speaks to the media on Tuesday. Photograph: Manuel Balce Ceneta/AP

In a Quinnipiac poll released on Tuesday, 75% of registered voters responding said that witnesses should be allowed to testify in the impeachment trial, versus 20% who did not want witnesses. Support for witness testimony included 49% of Republicans.

Congress was still digesting the news, reported by the New York Times on Sunday, that Bolton says Trump told him he wanted to keep withholding nearly $400m of security aid to Ukraine until officials there agreed to help investigate political rivals including former vice-president Joe Biden and his family.

On Monday night, the New York Times returned to the well, reporting that in the forthcoming book The Room Where It Happened, Bolton writes that he told the attorney general, William Barr, he was concerned Trump was doing personal favors for autocratic foreign leaders.

News of Bolton’s book has spurred some more moderate Republican senators – Mitt Romney of Utah and Susan Collins of Maine – to signal openness to supporting the calling of witnesses.

On Tuesday, the minority leader, Chuck Schumer, said the “drip, drip, drip” of information from Bolton’s manuscript was “reminiscent of Watergate”, the scandal that led to the resignation of Richard Nixon.

The longer it goes on, the more likely that more new evidence will come out that further implicates the president Chuck Schumer

Sekulow found another construction to describe the impeachment proceedings in his closing statement on Tuesday: “Danger, danger, danger.”

He said: “To lower the bar of impeachment based on these articles of impeachment would impact the functioning of our constitutional republic and the framework of that constitution for generations.

“To have a removal of a president based on a policy dispute? That’s not what the framers intended.”

While Trump’s lawyers have painted Trump’s alleged efforts to force the Ukrainian president to announce an investigation into Biden as a “policy”, Democrats have argued it amounted to election tampering, with the goal of providing Trump with a means to smear his potential 2020 rival.

Trump’s defense team could be pressed during the next question period of the trial to explain why not hearing from Bolton personally is preferable to calling Bolton, who has pre-emptively agreed to testify, as a witness.