Hillary Clinton backs gay marriage. A sign she's serious about 2016?

The declaration from former Secretary of State Hillary Clinton isn't a surprise. But backing gay marriage is likely a necessary step for any Democrat considering a 2016 run for president.

She may not be a declared candidate for president (yet). But Hillary Clinton is making it clear that she intends to continue to be part of the national political conversation. 

In her first public statement since stepping down as secretary of State, Mrs. Clinton has issued an official declaration of support for gay marriage.

In a video released by the Human Rights Campaign, she says: "LGBT Americans are our colleagues, our teachers, our soldiers, our friends, our loved ones, and they are full and equal citizens and deserve the rights of citizenship. That includes marriage. That's why I support marriage for lesbian and gay couples. I support it personally and as a matter of policy and law."

This is not an unexpected position for Clinton to take, nor is it likely to be controversial. If anything, she's just a bit late to the party. President Obama, of course, has already endorsed gay marriage, as has Vice President Joe Biden, Senate Majority Leader Harry Reid, and House Minority Leader Nancy Pelosi – along with pretty much every Democrat currently eyeing a 2016 run.

Clinton's husband, former President Bill Clinton, made clear that he supported gay marriage back in 2009. Mr. Clinton also recently published an op-ed declaring that he now believes the Defense of Marriage Act (DOMA) – which he signed into law back in 1996, and which is now being challenged before the Supreme Court – is unconstitutional. 

When Mrs. Clinton ran for president in 2008, her official position (like Mr. Obama's) was to favor civil unions, not gay marriage, saying she thought the matter should be left to the states. In response to a Human Rights Campaign questionnaire in 2007, she said she favored repealing the plank of DOMA that would deny federal benefits to couples in states that recognize gay marriage.

Since then, however, public opinion has continued to shift rapidly. With recent polls showing a majority of Americans overall now support gay marriage outright – including nearly three-quarters of Democrats – it's probably safe to say that all Democratic candidates for president will have to support gay marriage going forward, if they want to win their party's nomination.

Still, it's noteworthy that Clinton chose this moment to make her support for marriage equality official. It's been just over a month since she left the State Department, and while she is officially "taking time off," she also seems to be making it clear that she does not intend to lay low for long. Polls show she'd be a formidable – perhaps unbeatable – candidate for the Democratic nomination in 2016, and her uber-heavyweight status has essentially frozen the race for other Democratic hopefuls, who are waiting to see what Clinton decides before making their own plans.

Former Obama adviser David Plouffe echoed that view in a talk over the weekend, saying of Clinton: "She is, in both parties right now by far, I think, the most interesting candidate, probably the strongest candidate."  

One reason Clinton is seen as so strong, aside from her personal popularity, is her fundraising prowess. But it's worth noting on that front that making her support for gay marriage official was almost certainly going to be a necessary step for many of her wealthy Hollywood donors. Now she's checked that box. 

The issue of gay marriage is far more contentious for Republicans. The party's base is still strongly opposed to gay marriage, but many party strategists recognize that the issue is hurting the GOP among young voters, who tend to support it, and who will, by definition, play a larger and larger role in future elections.

The Republican National Committee's much anticipated "autopsy," released Monday, stated flatly: "For the GOP to appeal to younger voters, we do not have to agree on every issue, but we do need to make sure young people do not see the Party as totally intolerant of alternative points of view. Already, there is a generational difference within the conservative movement about issues involving the treatment and the rights of gays — and for many younger voters, these issues are a gateway into whether the Party is a place they want to be. If our Party is not welcoming and inclusive, young people and increasingly other voters will continue to tune us out."  

Recently, more and more Republicans have been expressing support for gay marriage. Last month, dozens of top GOP officials signed on to an amicus brief submitted to the Supreme Court in favor of overturning California's Proposition 8, a ballot initiative barring gay marriage. Just last week, Ohio Sen. Rob Portman – who had been on Mitt Romney's short list for the vice presidential nomination – announced he now supports gay marriage, explaining that his son is gay and that he wants him to be able to experience the "joy and stability of marriage."

Ironically, the "leave it up to the states" position that was once held by Democrats like Clinton is now being increasingly adopted by Republicans. As Florida Sen. Marco Rubio – seen as a frontrunner for his party's 2016 nomination – said over the weekend at the Conservative Political Action Conference (CPAC): "Just because I believe that states should have the right to define marriage in the traditional way does not make me a bigot."