Maine’s U.S. Sen. Susan Collins announced her support for same-sex marriage for the first time on Wednesday, hours after the nation’s largest gay-rights group endorsed her for re-election this year over Democrat Shenna Bellows, a longtime activist for same-sex marriage.

Collins has previously declined to say where she personally stood on the issue of same-sex marriage, arguing instead that it was an issue best handled at the state level.

On Wednesday, however, Collins’ campaign issued a statement that many in the gay rights community had expected to come much earlier from a lawmaker viewed as one of Congress’ friendliest Republicans on lesbian, gay, bisexual and transgender (LGBT) issues.

“A number of states, including my home state of Maine, have now legalized same-sex marriage, and I agree with that decision,” Collins said. “Today, same-sex couples can be legally married in 19 states and the District of Columbia. Nearly 44% of Americans live in a state where same-sex couples can be legally married, and I believe this number will only continue to grow.”

Earlier Wednesday, Collins once again picked up the endorsement of the Human Rights Campaign, which is the largest LBGT advocacy organization in the nation. Collins spokesman Lance Dutson said the announcement was in response to reporters’ renewed questions about her stance, and was “absolutely not” tied otherwise to the endorsement.

The Human Rights Campaign’s endorsement was not a surprise.

Human Rights Campaign endorsed Collins in both 2002 and 2008 and gave her an 82 out of 100 in its last congressional voting scorecard – higher than every other Senate Republican, most of whom scored either a zero or a 15. The organization has frequently praised her in the past for her support of LGBT issues.

“Senator Susan Collins has played a pivotal role in advancing support for LGBT equality – from her dogged support for the repeal of ‘Don’t Ask, Don’t Tell’ to her critical vote for the Employment Non-Discrimination Act last year,” Chad Griffin, president of the Human Rights Campaign, said in a statement. “HRC is proud to stand with Senator Collins, and with allies on both sides of the aisle like her, because she firmly believes that every American should be evaluated based on their abilities, and not who they love.”

While not unexpected, the endorsement was a clear disappointment to the campaign and supporters of her challenger this November, Democrat Shenna Bellows.

As the head of the American Civil Liberties Union of Maine, Bellows served seven years on the executive committee that organized the 2009 and 2012 referendums to legalize same-sex marriage in Maine. Bellows was frequently a spokeswoman during those campaigns as well.

She also lobbied the Legislature on numerous LGBT issues over the years. And as she points out in campaign speeches and materials, Bellows and her husband even delayed their own marriage until after same-sex couples could also legally wed in Maine beginning in December 2012.

“I’ve been proud and very privileged to be a leader in the LGBT equality movement for many years,” Bellows said. “As executive director of the ACLU of Maine, I spent every day bringing Republicans and Democrats together to expand civil liberties and strengthen equal protection under the law.”

In an interview, Bellows said she was not surprised by the Human Rights Campaign’s endorsement, calling it an election-year decision. In a swipe at Collins, she said she would provide “proactive representation and to expand Constitutional protections for our LGBT community.”

Same-sex marriage proponents have made dramatic gains in recent years, both in the courts and in political circles. Same-sex marriage is now legal in 19 states plus Washington, DC, while judges have ruled in favor of gay and lesbian couples in a dozen more.

Many observers expected Collins to endorse same-sex marriage last year as other members of Congress – including a few Republicans – announced their support amid shifting public attitudes. But Collins steadfastly remained mum on the issue or said she believed states should make that call, whether through voter referendums or legislation.

At the same time, Collins was praised by organizations such as the Human Rights Campaign for focusing on other issues important to the LGBT community – including several measures tied to same-sex marriage.

For instance, she fought to extend federal benefits to the same-sex partners of government employees and twice opposed Constitutional amendments to prohibit same-sex marriage.

Collins was a key broker in arranging a Senate vote to end the military’s “Don’t Ask, Don’t Tell” policy that prohibited openly gay service members. She also co-sponsored legislation to prohibit federal prosecutors from discriminating against LBGT jurors in federal trials and to treat same-sex “permanent partners” the same as heterosexual married couples in immigration cases.

Bellows criticized Collins for not speaking out on the LGBT community’s most significant policy fight during the 2009 and 2012 campaigns in Maine.

“I believe in taking strong stances in favor of Constitutional protections and equal rights even when they’re unpopular,” Bellows said. “Remaining silent on some of the biggest civil rights issues of our generation, even after the voters have spoken, isn’t leadership, and it isn’t how Maine became one of the most inclusive states in the country for LGBT rights.”

But Gregory Angelo, executive director of the Log Cabin Republicans organization that represents gay and lesbian Republicans, said Collins’ support for same-sex marriage is another sign that “the dam has finally broken.”

“As a longtime ally of Log Cabin Republicans who championed repeal of the flawed ‘Don’t Ask Don’t Tell’ policy and most recently the Employment Non-Discrimination Act, Senator Collins’ declaration of support for civil marriage equality is the latest milestone in a career that has exhibited bold and unwavering support for the LGBT community,” Angelo said.