Illinois Republican U.S. Senator Mark Kirk announced Tuesday that he now supports same-sex marriage, explaining in an interview that his personal relationships with gay friends – and the movie Lincoln – inspired him to switch his stance on the issue.

“Most of us have gay acquaintances at work or at church,” Kirk said in an interview with the Illinois Radio Network Tuesday, a copy of which was provided to WBEZ. “And the thought of legally discriminating against our own friends and coworkers is an anathema to me.”

During his first interview since issuing a four-sentence statement on his website Tuesday, Kirk told an IRN reporter that he was “pretty influenced” by Steven Spielberg’s Oscar-winning film about President Abraham Lincoln’s fight to end slavery.

“As a Republican leader, my job is to make sure that each generation is more free and has more dignity as an individual, which is a unique gift [from] the United States to the world,” Kirk said, adding that banning same-sex marriage is “against that Lincoln tradition.”

Kirk, the highest-ranking GOP elected official in Illinois, had previously steered clear of staking out a hard public stance on gay marriage. But his thinking has been evolving, and Kirk pointed to his friendship with a high school friend, who is gay.

Kirk now becomes the second Republican in the Senate to buck the party line and publicly support same-sex marriage. Ohio Sen. Rob Portman reversed his prior stance earlier this month after revealing his son is gay.

But on Tuesday, Kirk also told IRN he thinks gay marriage should be left to individual states, not the federal government.

“I would hope that we would restrain our appetite for power in Washington and not take over marriage law for the whole country,” Kirk said.

Kirk’s office declined an interview request from WBEZ on Tuesday.

The senator’s statement marks the first time Kirk has publicly announced his full support of same-sex marriage, though his office has said the senator’s views on the issue have been evolving for some time.  Behind the scenes, Kirk has been using his influence as Illinois’ highest-ranking Republican elected official to urge members of his party not to make too much noise in opposing same-sex marriage, which is an increasingly popular issue among key voting blocs.

In January, Kirk announced his support for embattled Illinois Republican Party Chairman Pat Brady. A handful of GOP bosses began working to fire Brady after he bucked the party line and came out in favor of same-sex marriage. They had enough support to call a special meeting in early March, where some had hoped to vote him out. But Kirk began working the phones the day before the meeting, urging State Central Committee members not to oust Brady. The meeting was cancelled just hours before it was scheduled to start.

Also, in a February interview with WBEZ, Kirk repeatedly dodged questions about whether he supported a same-sex marriage bill now pending in the General Assembly. He instead pointed to other votes he’s taken in favor of gay rights, such as one to end the ban on gays serving openly in the military.

With Kirk’s support, same-sex marriage backers would appear to have a 50-vote bloc in the U.S. Senate, with a handful of Democrats who have remained silent on the issue.

Legislation legalizing same-sex marriage in Illinois is currently pending in the state House of Representatives. The state Senate approved the bill earlier this year by a vote of 34-21. Members of the House sponsoring the measure have said they will call the bill for a vote when they know they have the minimum votes. House Speaker Michael Madigan has said proponents of same-sex marriage still need a dozen representatives to sign on to the plan. Gov. Pat Quinn has said he would sign the bill into law if it’s passed.

Reporter Tony Arnold contributed to this story.