The White House expects several Republican senators to join Democrats in calling for witnesses in President Donald Trump’s upcoming impeachment trial, CBS News reported.

The report said senior White House officials expect at least four Republican senators, likely more, to break ranks with Senate Majority Leader Mitch McConnell on the issue.

Republicans have only a three-seat majority in the upper chamber, and if four or more GOP senators join Democrats in calling for witnesses, McConnell would likely be forced to cave on the matter.

The names White House officials threw out included Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, Mitt Romney of Utah, and Cory Gardner of Colorado.

If McConnell gives in to demands to call witnesses, it would dramatically alter the stakes of Trump’s trial by forcing top executive-branch officials – who have so far refused to testify – to reveal what they know to the public about the president’s efforts to solicit foreign interference in the 2020 election.

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The White House expects several Republican senators to join Democrats in calling for witnesses in President Donald Trump’s upcoming impeachment trial, CBS News reported.

House Speaker Nancy Pelosi withheld the two articles of impeachment against Trump while Democrats and Republicans fought over the terms of a trial, including over whether to call witnesses.

Senate Majority Leader Mitch McConnell said last week that the Senate would move forward with a trial without deciding on the question and instead address it once the trial starts, similar to the process that was set during former President Bill Clinton’s impeachment trial in the 1990s.

But last week, GOP Sen. Susan Collins of Maine told Maine’s Bangor Daily News she was working with a “fairly small group” of fellow Republican senators to ensure witnesses are called in Trump’s trial.

“We should be completely open to calling witnesses,” Collins said on Friday, according to the Bangor Daily News. “I am hopeful that we can reach an agreement on how to proceed with the trial that will allow the opportunity for both the House and the president’s counsel if they choose to do so.”

CBS News reported that White House officials believed at least four Republicans, likely more, would vote to call witnesses. The names the officials threw out included Collins, Sens. Lisa Murkowski of Alaska, Mitt Romney of Utah, and Cory Gardner of Colorado.

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Officials told CBS they were also bracing for Sens. Rand Paul of Kentucky and Lamar Alexander of Tennessee to break ranks.

The GOP has only a three-seat majority in the upper chamber. If four or more Republican senators call for witnesses, it’s likely McConnell would be forced to cave and give in to the demands.

Such a development could dramatically change the stakes of the president’s trial and force key officials – like Secretary of State Mike Pompeo, acting White House chief of staff Mick Mulvaney, and former national security adviser John Bolton – to testify before Congress and the public about their knowledge of Trump’s efforts to solicit foreign interference in the 2020 election.

After McConnell announced last week that the Republican-controlled upper chamber would not immediately commit to calling witnesses, Pelosi said she would transmit the articles of impeachment to the Senate this week.

But the House speaker’s move to withhold the articles in the first place appears to have paid off at least in part by spurring moderate and vulnerable Republican senators to publicly break with McConnell.

Democrats also notched another victory when Bolton announced he would be willing to testify in Trump’s trial, ratcheting up the pressure on McConnell to agree to call witnesses.

The two articles of impeachment against the president relate to his efforts to strong-arm Ukraine into delivering political dirt on one of his 2020 rivals, former Vice President Joe Biden, while Trump withheld vital military aid and a White House meeting that Ukrainian President Volodymyr Zelensky desperately wanted.

Trump’s actions came to light in a whistleblower complaint that an anonymous US intelligence official filed in August. At the center of the complaint was a July 25 phone call between Trump and Zelensky in which Trump repeatedly pressured Zelensky to investigate the Bidens and look into a bogus conspiracy theory suggesting that Ukraine interfered in the 2016 US election.

The White House released a memo of the phone call that confirmed the whistleblower’s main allegation. But subsequent testimony from nonpartisan career national-security and foreign-service officers showed that the phone call was just one data point in a monthslong campaign by Trump and his personal lawyer Rudy Giuliani to force Ukraine to accede to his demands.

Gordon Sondland, the US’s ambassador to the European Union, testified that “everyone was in the loop” on Trump’s efforts, including Bolton, Pompeo, Mulvaney, and other top brass at the White House and across federal agencies.