Story highlights The "nuclear option" lowered the threshold to overcome a filibuster from 60 to 51 votes

The decision to lower the threshold came after GOP obstruction on Capitol Hill

Washington (CNN) Three years after using the "nuclear option" to upend Senate tradition by effectively removing filibusters against most presidential nominations, Senate Democrats insisted Thursday they don't regret that decision, even as Donald Trump becomes president and they recognize they may be powerless to block controversial nominations.

"I have absolutely no regret," said Oregon Democratic Sen. Jeff Merkley, who led the charge to weaken the filibuster, freeing up scores of President Barack Obama's executive and judicial branch nominees. "We'd never seen abuse of advice and consent in the history of our country so that was a necessary way to correct it."

Frustrated by numerous GOP filibusters against Obama's nominees, Merkley and other junior Democrats in 2013 lobbied their leaders to change the rules. Senior Democrats initially were wary of the bold step, reminding their younger colleagues that they would not be in the majority forever and that the move could come back to haunt them.

But in November of that year, then-Senate Majority Leader Harry Reid and other top Democrats became convinced GOP delaying tactics were crippling Washington. They triggered the nuclear option which -- over the objections of Republicans -- lowered the threshold to overcome a filibuster from 60 to 51 votes.

"The supermajority was used as a tool to assault the executive branch and judicial branch and that was the only cure available was to make it a simple majority," recalled Merkley.

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