WASHINGTON -- Senate Republicans' loyalty to President Donald Trump could face its starkest test yet this week after John Bolton, the former national security adviser, reportedly wrote that Trump told Bolton he had blocked U.S. military aid to Ukraine in an effort to get Ukraine to investigate a Democratic rival.
The revelations, contained in a book draft, sent tremors through Capitol Hill on Monday morning hours before Trump's lawyers were set to resume their defense of the president, which began Saturday morning.
Sen. Mitt Romney, R-Utah, told reporters that "it's increasingly likely" that there will be enough votes to subpoena Bolton as a witness, as Democrats have demanded.
"The reports about John Bolton's book strengthens the case for witnesses and have prompted a number of conversations among my colleagues," said Sen. Susan Collins, R-Maine, another key moderate.
Even Sen. Lindsey Graham, R-S.C., a firm Trump ally who has opposed having any witnesses, suggested he would be open to some kind of agreement to bring in witnesses.
"If there is a desire and decision by the Senate to call Democratic witnesses, then at a minimum the Senate should allow President @realDonaldTrump to call all relevant witnesses he has requested," Graham tweeted.
Trump's lawyers have staked their defense in part on denying any link between the events at the heart of the impeachment case, which alleges that Trump abused his power by pressuring a foreign government to help his reelection campaign -- and then obstructed Congress by ordering aides not to testify or provide documents.
Trump's lawyers also have repeatedly declared that no witness had firsthand knowledge of a direct link between the White House order to withhold $391 million in congressionally authorized security aid and Trump's push for Ukraine to announce an investigation of Joe Biden, who is running for the Democratic presidential nomination, and his son Hunter.
The president denied Bolton's claims in a series of angry tweets that began after midnight and picked up again in the early morning.
"I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens," he wrote. "In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book."