Donald Trump's defence team concluded its oral arguments in the US Senate impeachment trial on Tuesday, setting the stage for two days of questioning. The closing arguments came amid a bombshell report that former national security adviser John Bolton implicates President Trump in his new book. Mr Bolton reportedly writes that Mr Trump directly withheld security aid to Ukraine for his own political benefit. The report added weight to the Democratic Party's call for witnesses. The president's Republican Party has tried to resist calls for witnesses to testify, largely out of concern over what Mr Bolton might say. Four Republicans would need to side with Democrats in a vote on whether new testimony will be heard. US media outlets reported on Tuesday that Mitch McConnell, the most senior Republican, had told his senators during a closed-door meeting that following the Bolton reports the party did not have the votes to hold off witnesses. But Mr McConnell and his leadership team were reportedly confident of pressuring enough Republican senators by the end of the week to win a vote. Defence rests The president's defence wrapped up its arguments early on Tuesday, having used around half of its allotted 24 hours over three days. Their approach was a contrast with that of the Democrats, who used all of their allotted time to present a detailed case against the president. Jay Sekulow, the president's personal lawyer, said: "The bar for impeachment cannot be set this low. Danger, danger, danger. These articles must be rejected. The Constitution requires it. Justice demands it." White House counsel Pat Cipollone concluded by calling on senators to "end of the era of impeachment for good". President Trump was impeached on charges of abuse of power and obstruction of Congress. He is accused of withholding $391m (£300m) in military aid, in an attempt to pressure Ukraine's President Volodymyr Zelensky to announce a corruption investigation into Mr Trump's Democratic political rival, Joe Biden. Mr Trump denies the allegations against him, and Republicans have argued that no first-hand witnesses have so far connected the president to a scheme to withhold aid for political benefit. The significance of the apparent revelations from Mr Bolton, first reported by the New York Times, is that they would undermine that argument. He reportedly says in his forthcoming book that he was instructed directly by the president to withhold the aid in order to pressure Ukraine. Mr Trump told reporters last week that he did not want Mr Bolton to testify, citing national security issues.