Former secretary of state Hillary Rodham Clinton's announcement -- via video -- this morning that she is personally and publicly supportive of allowing gay and lesbian couples to marry was a necessary political move as she continues to keep herself in the mix as a potential 2016 presidential candidate.

"I'm sure she's been there for awhile now, and politically it's imperative for a Democratic presidential aspirant, so her timing is perfect," said Steve Murphy, a Democratic consultant who ran former congressman Dick Gephardt's 2004 presidential bid.

In the video, which was released on the Human Rights Campaign Web site, Clinton details her work on behalf of gay rights as secretary of state. But, it's important to note that Clinton's position does mark a clear shift -- and represents the most obvious evidence yet that she wants to preserve the possibility of running for president in three years' time.

When she ran for president in 2008, Clinton -- like then-Sen. Barack Obama -- supported civil unions for gay couples but not same-sex marriage. Clinton acknowledges in the video that "my personal views have been shaped over time" and that her experiences as secretary of state  -- and as a mom -- influenced the change. (She also hints that serving as the country's top diplomat delayed her from announcing the change in her position.)

While we take Clinton at her word, there is considerable political reason for her to come out fully in support of gay marriage, too.

Democrats and Independents have moved strongly in favor of gay marriage in the last four years, and many of the people who may well challenge Clinton if she runs for president in 2016 have already staked out positions well to her ideological left on gay marriage -- before today, that is.

New York Gov. Andrew Cuomo was hailed as a hero by gay rights advocates when he spearheaded an effort to legalize same-sex marriage in 2011. Maryland Gov. Martin O'Malley received accolades when he signed a measure legalizing it in his state last year and fought to uphold it in a subsequent referendum campaign. Vice President Biden caught much of the political world off-guard when he announced his support for gay marriage, even before President Obama did.

Even members of Clinton's famous family were already publicly supportive of gay marriage. Former president Bill Clinton penned an editorial earlier this month opposing the Defense of Marriage Act, which he signed into law, and Chelsea Clinton is also supportive of allowing gay people to marry.

The simple fact is that Clinton needed to get on the right side of the gay marriage issue -- in a public and decisive way. Questions were already being asked about why she had not clarified her position on the issue -- particularly after her husband's op-ed.

Remember that the biggest danger for Clinton's political future is that she is cast as someone without a core set of beliefs, a perennial late-arriver on issues of importance to the Democratic base. That perception is what hurt her so badly -- and empowered Obama -- during the 2008 presidential campaign when it came to the issue of the war in Iraq.

The longer Clinton waited to get right on same-sex marriage, the more she opened herself up to that critique. She now puts that potential attack behind her, and preserves herself as the very clear front-runner for the 2016 Democratic presidential nomination.

Sean Sullivan contributed to this report