Minority Leader Chuck Schumer has asked that the Senate trial of Donald Trump call new witnesses, and Speaker of the House Nancy Pelosi is backing him up -- delaying send the impeachment to the Senate until she knows what the rules of the Senate trial will be. Majority Leader Mitch McConnell doesn't want that. He wants a short trial with no new witnesses.
McConnell may have to give on this, because the majority of the public agrees with Schumer. About 54% of voters want more witnesses called (including 66% of Democrats and 51% of Independents). Only 27% say no new witnesses should be called. Even a plurality of Republicans want to see more witnesses (43% to 39%).
Denying the right to call more witnesses is just going to make the Senate trial look rigged -- an unfair debacle designed to protect Trump by his party. Republican senators are going to have a tough time trying to defend that in the next election (which is now less than a year away).
The chart above is from the Morning Consult Poll -- done on December 19th and 20th of a national sample of 1,387 registered voters, with a 3 point margin of error.