Collins and Murkowski are seen as moderates and their support for this approach and backing the GOP is a huge win for McConnell.
Even though the House of Representatives voted to impeach President Donald Trump, Speaker Nancy Pelosi (D-CA) has held onto the articles of impeachment. She has continually demanded that the Senate impeachment trial is "fair," which Democrats argue means calling witnesses to testify.
Senate Majority Leader Mitch McConnell (R-KY) has refused to comply with the Democrats' demands, especially since the Senate is under his control, not Nancy's. The Democrats needed four Republicans to vote in line with them in order to call witnesses. But it's looking like that won't be happening after all.
According to The Hill, McConnell has the votes to keep the Senate trial short, meaning new witness testimony and documents would not be included. Two of the moderate Republicans – Sens. Susan Collins (R-ME) and Lisa Murkowski (R-AK) – are voting siding with McConnell.
Both Collins and Murkowski believe the precedent set during the Clinton impeachment trial should be followed. They want to see House impeachment managers and Trump's defense team make their opening statement. Then, if necessary, the Senate could subpoena for additional documents and witness testimony.