Hillary Rodham Clinton finally declared her support for marriage equality for gay couples on Monday. But her decision to do so now is being interpreted by many as a signal she may be seriously weighing a 2016 presidential run, and attempting to defuse an issue that made her look too politically cautious to win the Democratic nod in 2008.

Clinton's chief Democratic rivals all endorsed same-sex marriage as far back as seven years ago, and the issue is widely popular with both Democratic and independent voters.

By weighing in at last and throwing her support behind same sex marriage two years before the next presidential primary, Clinton may be hoping that the issue will be settled among Democrats, if she should decide to run.

In the November 2016 general election the Democratic nominee is virtually certain to support same-sex marriage, and despite increasing soul and poll searching, there's still a strong possibility the Republican nominee will not.

That could make hostility to same sex marriage a defining wedge issue for the GOP nominee. It could have major political costs. A poll released on Monday shows a dramatic shift in public attitudes about legalizing same sex marriage, with 58 percent of Americans now supporting it. Three years ago, the figure was 47 percent, the ABC News/Washington Post poll reported.

Seventy-two percent of Democrats, 62 percent of independents and only 34 percent of Republicans support same-sex marriage, the latest ABC-Post poll found. If Republican opinions do not change significantly on the issue in the next two years, a GOP presidential hopeful may find the position causes considerable problems in the November general election.

Clinton recently stepped down as secretary of State, freeing her to talk more openly about U.S. domestic political matters. But even close observers cannot tell if it indicates her intention to throw her hat in the ring in 2016.

'I have no idea whether she is going to run or not,' veteran strategist Jim Manley told the New York Times. 'All I know is that she was going to have to make this move quickly after stepping down as secretary of State if she was even going to think about it.'

Same-sex marriage is now legal in nine states and the District of Columbia. Civil unions are legal in eight more states, with Colorado on the verge of joining. Many other states have outlawed gay marriage.

Clinton's 2002 Senate vote authorizing an invasion of Iraq lost her major support among progressives, particularly as the war professed. In contrast President Obama, as an Illinois state legislator, had condemned the war from the start. As the 2008 primaries approached, Clinton lost valuable political ground to the lesser-known lawmaker from Illinois over the issue.

With major Democratic politicians now taking a similar stand on gay marriage, the issue may not play the type of role in 2016 that the Iraq war played in 2008, but the likely contrast from the GOP will be telling.

Some gay activists were leery of Clinton's sudden endorsement of same sex marriage on Monday. President Bill Clinton signed Don't Ask, Don't Tell in 1993 and the Defense of Marriage Act in 1996, with both bills seriously impacting the lives of millions of gay and lesbian Americans. DOMA requires the federal government to refuse to recognize same-sex marriages, still stripping gay couples of legal protections at the federal level.

Support for marriage equality is becoming a mainstream position among Democrats, but the issue is increasingly leading to a divisive war of words among Republicans. Senator Rob Portman of Ohio last week became the only Republican senator to support legalizing same-sex marriage and he did so after learning that one of his adult sons is gay.

Former Secretary of State Hilary ClintonGoogle Images