Sen. Claire McCaskillClaire McCaskillUnder pressure, Dems hold back Gorsuch support Overnight Defense: General warns State Department cuts would hurt military | Bergdahl lawyers appeal Trump motion | Senators demand action after nude photo scandal The Hill’s Whip List: Where Dems stand on Trump’s Supreme Court nominee MORE (D-Mo.) announced her support for same-sex marriage Sunday night, becoming one of the first Democratic senators from a traditionally Republican state to do so.

McCaskill's statement, posted to her Tumblr page, precedes oral arguments at the Supreme Court on Tuesday and Wednesday on a pair of cases examining states' and the federal government's ability to define marriage as between a man and a woman.

"I have come to the conclusion that our government should not limit the right to marry based on who you love," McCaskill wrote. "While churches should never be required to conduct marriages outside of their religious beliefs, neither should the government tell people who they have a right to marry."

ADVERTISEMENT
McCaskill, who was reelected to a second term in the Senate last year, joins a growing number of lawmakers advocating for same-sex marriage. Earlier this month, Republican Sen. Rob PortmanRob PortmanOvernight Finance: Senators spar over Wall Street at SEC pick's hearing | New CBO score for ObamaCare bill | Agency signs off on Trump DC hotel lease GOP senators offer bill to require spending cuts with debt-limit hikes Vulnerable Senate Dem: Border tax concerning for agriculture MORE (Ohio) switched his position in favor of same-sex marriage, citing his college-aged son who is gay.

Former Secretary of State Hillary ClintonHillary Rodham ClintonWarren: 'Today is a great day... but I'm not doing a touchdown dance' Hollywood stars weigh in on GOP pulling healthcare bill Hillary Clinton: Today was a victory, 'but this fight isn't over yet' MORE made a splashy endorsement of gay marriage last week, reflecting the broader shift the Democratic Party has made on the issue in recent years. 

In her post, McCaskill says she was influenced by friends and colleagues in committed, same-sex relationships.

"My views on this subject have changed over time, but as many of my gay and lesbian friends, colleagues and staff embrace long term committed relationships, I find myself unable to look them in the eye without honestly confronting this uncomfortable inequality," McCaskill wrote. "Supporting marriage equality for gay and lesbian couples is simply the right thing to do for our country, a country founded on the principals of liberty and equality."

ADVERTISEMENT
She also acknowledges that attitudes on gay marriage seem to be shifting. A Washington Post / ABC News poll released last week showed that 58 percent of Americans backed gay marriage, an all-time high.

"Good people disagree with me," McCaskill said. "On the other hand, my children have a hard time understanding why this is even controversial. I think history will agree with my children."