At least four or more Republicans could vote to allow witnesses at President Donald Trump's Senate impeachment trial, according to senior White House officials who spoke to CBS News.

The senators being looked at as potential defectors include Lisa Murkowski of Alaska, Susan Collins of Maine, Mitt Romney of Utah and Cory Gardner of Colorado, CBS News reported.

White House officials also view Rand Paul of Kentucky and Lamar Alexander of Tennessee as two additional GOP senators who may potentially break party ranks, CBS News reported.

A steady drumbeat of GOP senators has come forward in recent days to voice approval for allowing testimony from witnesses despite proposals to change Senate rules and dismiss the articles.

Alexander said Tuesday he would vote against a motion to dismiss the case and called for a guaranteed vote on allowing witnesses and seeing additional documents.

Sen. Lamar Alexander said Tuesday he would vote against a motion to dismiss the case and called for a guaranteed vote on allowing witnesses and seeing additional documents. “I would vote against a motion to dismiss,” he said in a statement. “I think we should hear the case. We have a constitutional duty to do that.”

Credit: Tom Williams

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Credit: Tom Williams

“I would vote against a motion to dismiss,” he said in a statement. “I think we should hear the case. We have a constitutional duty to do that. That means to me, number one, hear the arguments. Number two, to ask our questions. Number three, to be guaranteed the right to vote on whether we need additional evidence following hearing the case. Evidence could be witnesses; it could be documents.”

Senate Majority Leader Mitch McConnell announced Tuesday that the Senate trial will likely begin next Tuesday, adding he does not have the votes to dismiss the articles, as Trump has previously suggested.

“There is little or no sentiment in the Republican conference for a motion to dismiss,” McConnell said Tuesday. “Our members feel we have an obligation to listen to the arguments.”

Other senators agreed with McConnell’s assessment.

“I think our members generally are not interested in the motion to dismiss. They think both sides need to be heard,” said Sen. Roy Blunt, R-Mo., who is part of GOP leadership.

McConnell has said recently the full Senate would vote on whether to call witnesses after the trial begins.

Republicans control the Senate 53-47. A motion to call witnesses in the trial requires 51 votes, meaning four of the 53 Republicans in the Senate would need to break ranks and join Democrats on the issue.

Last week, Collins said she was working with a "fairly small group" of GOP senators to allow testimony in the trial.

“My position is that there should be a vote on whether or not witnesses should be called,” Collins said.

Romney said he was interested in hearing testimony from Trump's former national security adviser John Bolton, who said he would testify if subpoenaed.

Sen. Mitt Romney said he was interested in hearing testimony from Trump's former national security adviser John Bolton, who said he would testify if subpoenaed.  "I've said I'd like to hear from John Bolton," Romney said Monday. “I expect that barring some kind of surprise, I'll be voting in favor of hearing from witnesses after those opening arguments.”

Credit: KIM RAFF

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Credit: KIM RAFF

"I've said I'd like to hear from John Bolton," Romney said Monday. “I expect that barring some kind of surprise, I'll be voting in favor of hearing from witnesses after those opening arguments.”

White House officials said the president intends to claim executive privilege, if necessary, to block Bolton from testifying, according to CBS News.

White House officials said President Donald Trump intends to claim executive privilege, if necessary, to block former national security adviser John Bolton from testifying.

Credit: ERIN SCHAFF

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Credit: ERIN SCHAFF

Murkowski said last week the Senate should vote to allow witnesses.

“I've been working to make sure that we will have a process that we can take a vote on whether or not we need additional information, and yes, that would include witnesses,” Murkowski said.

The House is scheduled to vote Wednesday on sending Trump’s articles of impeachment over to the Senate, according to The Associated Press.