WASHINGTON, D.C. -- A third Senate Democrat has announced his intention to vote for Judge Neil Gorsuch, President Trump's Supreme Court nominee.

"After meeting with Judge Gorsuch, conducting a thorough review of his record, and closely following his hearing before the Senate Judiciary Committee, I believe that he is a qualified jurist who will base his decisions on his understanding of the law and is well-respected among his peers," Indiana Sen. Joe Donnelly said in a statement.

Donnelly joins Democratic colleagues Sens. Joe Manchin of West Virginia and Heidi Heitkamp of North Dakota, who both pledged last month to vote to confirm Gorsuch, slated to take the seat held by Justice Antonin Scalia, who died in February 2016.

Both Donnelly and Heitkamp bemoaned the fact that Judge Merrick Garland, President Obama's nominee to replace Scalia, never got an up-or-down vote.

"I was deeply disappointed by the way the most recent Supreme Court nominee, Judge Garland, was treated by the Senate, but as Senator, I can only vote on the nominee that comes to the Senate floor," Donnelley said.

"However, I believe that we should keep the current 60-vote threshold for Supreme Court nominees," he added.

Without invoking the so-called nuclear option -- changing the Senate rules to allow lawmakers to end a filibuster with a simple majority, 51 votes, rather than the current threshold of 60 -- Republicans need at least five more Democrats to agree to vote for cloture.

But according to Senate Majority Leader Mitch McConnell, who on Sunday refused to rule out the nuclear option, Gorsuch will be confirmed, on way or another, by Friday.

"Judge Gorsuch is going to be confirmed. The way in which that occurs is in the hands of the Democratic minority," McConnell told Fox News' Chris Wallace.

"I don't think we know" whether additional Democrats will sign on to avoid a filibuster -- a move Democratic Leader Chuck Schumer of New York vowed to carry out last month, McConnell added.

It was Democrats who invoked the nuclear option in 2013, then to allow confirmation of lower court judges.

Schumer has since said he regrets the decision, which he says he argued against four years ago. McConnell, who spoke out against the nuclear option in 2013, now says that "going nuclear" prevents inappropriate filibustering by the minority party.

ABC News' Ali Rogin contributed to this report.