WASHINGTON (Reuters) - Republican U.S. Senator Mark Kirk, facing a tough re-election fight in Illinois, said on Monday the Senate should vote on whomever President Barack Obama nominates to the U.S. Supreme Court, breaking with his party’s leadership.

Republican U.S. Senate candidate Mark Kirk of Illinois speaks to supporters after beating Democratic nominee Alexi Giannoulias for the Senate seat formally held by U.S. President Barack Obama, at an election night rally in Wheeling, Illinois November 2, 2010. REUTERS/Jeff Haynes

In another defection among Republicans, Senator Susan Collins of Maine called for hearings on the eventual nominee.

A political fight has erupted over filling the court’s vacancy left by the Feb. 13 death of conservative Justice Antonin Scalia, with many top Republicans threatening to block any nominee put forth by the Democratic president.

Obama’s nominee could shift the court to the left for the first time in decades.

Senate Majority Leader Mitch McConnell has said the seat should remain vacant until Obama’s successor takes office in January so voters can have a say on the selection when they cast ballots in the November presidential election.

Kirk wrote in a Chicago Sun-Times opinion piece that he recognized the right of any president to choose a Supreme Court nominee and he looked forward to Obama picking one for the Senate to consider for confirmation.

“I also recognize my duty as a senator to either vote in support or opposition to that nominee following a fair and thorough hearing along with a complete and transparent release of all requested information,” Kirk added.

Kirk, who holds Obama’s old Senate seat, said he hoped the president would pick a nominee “who can bridge differences, a nominee who finds common ground and a nominee who does not speak or act in the extreme.”

Kirk’s stance illustrates that McConnell may have trouble keeping Senate Republicans fully united over filling Scalia’s seat. Some senators like Kirk are seeking re-election this year in states where Democrats are competitive.

Collins, who is not facing re-election until 2020, said on Monday the Senate had an obligation to hold public hearings on Obama’s nominee.

“The kind of thorough process that a hearing allows is the best way to evaluate a nominee,” Collins told reporters, according to the Hill newspaper.

But it appeared unlikely that enough Republicans would peel away from McConnell to allow a vote on the Senate floor.

Republican Senator Orrin Hatch of Utah said on Monday it was up to McConnell and Judiciary Committee Chairman Chuck Grassley to decide whether to hold confirmation hearings.

“I feel like we ought to put it off and get it out of this harsh atmosphere,” Hatch told reporters.