Mitch McConnell is expected to move quickly to acquit President Donald Trump if a closely watched vote planned for Friday to compel witnesses

Mitch McConnell privately said earlier Tuesday that he wasn't sure there were enough Republican votes to block more witnesses, given that some moderates in the GOP's 53-47 Senate majority were wavering.  Any witness resolution would likely require four Republican defections in the Senate, because in the event of a 50-50 tie, Chief Justice of the United States John Roberts is highly likely to abstain rather than assert his debatable power to cast a tie-breaking vote.
Late Tuesday night, a Senate leadership source told CNN that Republicans were specifically assessing the viability of two alternative options.
One plan is to amend any resolution calling for a particular witness to also include a package of witnesses that assuredly wouldn't win enough support in the Senate. For example, if the Democrats seek to call former National Security Advisor John Bolton, Republicans might seek to question Hunter Biden over his lucrative board position in Ukraine, and Rep. Adam Schiff over his inconsistent statements concerning his panel's contacts with the whistleblower at the center of the impeachment probe.

CBS’s Nancy Cordes describes what she’s hearing and suggests the argument being used by McConnell and other Republicans is that if the president is going to be acquitted, then why even call witnesses and drag this out for weeks when it ultimately won’t matter:

Just fyi, ignore the statement that “Republican leadership does not believe they have the votes to block witnesses at this time” in the tweet. I was ready to report that as recent, but after watching the video, Cordes was clearly just repeating what McConnell said last night in the video and not proclaiming this as a recent statement from Republican leadership.