So Hillary Clinton released a video this morning announcing that she now formally supports gay marriage. There have been lots of questions about Clinton’s motives and timing here, but here’s why the timing is actually a good thing: It comes just as the Supreme Court is preparing to hear two gay marriage cases, with potentially far reaching consequences for the future of marriage equality.

Here’s Clinton’s video — it’s strong, nuanced stuff:

Though Clinton endorsed New York’s gay marriage law in 2011, and has repeatedly spoken out for gay rights in the past, as Steve Benen details, Clinton’s announcement today moves the ball significantly. Every act that demonstrates that the culture is changing, and is ready for legalized gay marriage, could prove helpful, since most legal observers believe the Supreme Court won’t want to get too far out ahead of public opinion in its rulings on the Defense of Marriage Act and Proposition 8 cases. In confirming that no Dem presidential candidate will ever be viable without embracing marriage equality, Clinton is sending a strong message to the Court that the American public is ready to embrace it. What’s more, note when it comes to the legal right to marriage for gay and lesbian Americans, Clinton’s language is unequivocal:

“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, embedded in a broader effort to advance equality and opportunity for LGBT Americans and for all Americans.”

With the claim that “the rights of citizenship” include “marriage,” Clinton is effectively arguing that there is a Constitutional right to gay marriage. This goes even farther than the Obama administration’s legal brief in the Prop 8 case went. That brief argued that Prop 8 is unconstitutional because it must be subjected to “heightened scrutiny” and that so doing reveals it to violate the Constitution’s equal protection clause. That’s a bold argument, but it stops just short of arguing that gay marriage is a constitutional right. Clinton took that final step.

Every little thing along these lines makes it that much more likely that the High Court will adopt a sweeping ruling in the Prop 8 case — one arguing that Prop 8 is unconstitutional, which would give advocates a powerful weapon to topple other state laws around the country that outlaw gay marriage. It’s particularly helpful having this case made by a woman who until very recently was the public face of American diplomacy with the rest of the world.

By the way: If you want to know why many of us pushed Obama so hard to come out for gay marriage, today helps explain it. In so doing, Obama essentially made it impossible for any Democratic nominee for president not to publicly embrace full equality. This — combined with polls demonstrating the public’s rapid evolution on the issue — is already putting more pressure on the GOP to evolve on the issue already, too, as evidenced by the heartening show of support for gay marriage at the Conservative Political Action Conference. A sweeping ruling from the High Court would of course push this process along in a big way. Every little bit helps make such a ruling more likely — which is to say, every little bit helps put anti-gay-marriage laws, a relic of legalized bigotry, on the path to extinction.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.