WASHINGTON — Democrats quickly enjoyed the first fruits of a milestone Senate vote making it harder for the Republican minority to block President Barack Obama’s nominations: They swiftly ended a GOP filibuster against one of his top judicial selections and prepared to do the same for two others.

Over the longer term, they might regret what they did and how they did it, Republicans and others are warning.

When Democrats muscled the changes through Thursday over the opposition of every GOP senator, it helped heighten Congress’ already high level of partisan animosity. Senate Majority Leader Harry Reid, D-Nev., used a process that let Democrats unilaterally weaken the filibuster by simple majority vote, rather than the two-thirds margin usually used for major changes in chamber rules, which would have required GOP support.

“If the majority can change the rules, then there are no rules,” said veteran Sen. John McCain, R-Ariz., who has resisted similar changes in the past. “It puts a chill on the entire U.S. Senate.”

Such comments suggested a further erosion in the mutual trust the two parties would need to tackle sensitive, large-scale issues like still-massive budget deficits and a tax system overhaul. The tensions also won’t help Congress’ efforts early next year to avoid another government shutdown and prevent a federal default, twin disputes that the two parties struggled to resolve this fall.

And even though Thursday’s change left intact the rule requiring 60 Senate votes to end filibuster on legislation, it raised an obvious question: Might a future Senate majority, hitting obstacles advancing a president’s agenda, ram through changes weakening filibusters against bills too?

In control of both the White House and Congress someday, Senate Republicans might be tempted to force a filibuster change to cover legislation and use it, for example, to repeal Obama’s health care law.

“I don’t think this is a time to be talking about reprisals,” Senate Minority Leader Mitch McConnell, R-Ky., said after the vote. He said later, “The solution to this problem is at the ballot box. We look forward to having a great election in November 2014.”

McConnell spoke after the Senate voted 52-48 to allow a simple majority vote to end filibusters, instead of the 60 votes required since 1975. The change affects nominees for top federal agency and judicial appointments, but not Supreme Court justices.

Republicans had warned repeatedly that should they win Senate control, they will happily use the diluted filibuster to win Senate approval for future nominees by GOP presidents that Democrats might have blocked.

“The silver lining is that there will come a day when the roles are reversed,” said Iowa Sen. Charles Grassley, top Republican on the Senate Judiciary Committee. He warned that when his party wins a Senate majority they likely will apply the 51-vote filibuster threshold to a Republican president’s Supreme Court nominees.