The bang you just heard was the gay marriage issue detonating in Pennsylvania, where, politically speaking, Attorney General Kathleen Kane has really put the screws to Gov. Tom Corbett.

What happened yesterday was a textbook fusion of high principle and shrewd politics. Kane, a Democrat elected last November as the state's chief law-enforcement official, announced that she won't defend the Pennsylvania ban on gay marriage ("I ethically cannot do that as a lawyer"), because that ban, currently being challenged in a federal lawsuit, is, in her words, "wholly unconstitutional."

And she's right about that. The Fourteenth Amendment to the U.S. Constitution says that "no State shall...deny to any person within its jurisdiction the equal protection of the laws." Anyone with even basic reading skills will quickly discover, in the lawsuit, that the 23 aggrieved Pennsylvania residents, including 10 gay couples, are being treated as ill-protected second-class citizens.

Kane's stand against bigotry gives a powerful symbolic boost to that lawsuit, which was filed in federal court earlier this week by the ACLU. But her principled position also packs a political punch. She was elected last November to break the mold - she outperformed all the men on the state ballot - and she's fulfilling her promise to be what she called "an independently elected voice." She's in sync with the evolving public mood - in the latest polls, Pennsylvanians favor gay marriage by 52 to 41 percent, a stunning 19-point swing since 2006 - and by refusing to defend the ban in court, she has cemented her rep as a gadfly who defies the good old boys.

And good old boy numero uno is Tom Corbett, the Republican governor who's sagging in the polls on the eve of his re-election bid. By bailing on the lawsuit, Kane has put him in a heckuva bind.

It's a quandary of risk versus reward. Corbett could decide to defend the gay marriage ban - his general counsel, James Schultz, could do the honors - because his conservative base will virtually demand it. If Corbett were to bail on the ban, the base would bail on him. His '14 bid for a second term would be doomed.

On the other hand, how can an unpopular conservative male possibly expect to win over the swing voters in the populous suburban Philadelphia suburbs if he's in court defending bigotry? A Democratic opponent like Allyson Schwartz would hang that one around his neck.

The shrewdness of Kane's chessboard move is best measured by Team Corbett's pained wailing. Schultz, the general counsel, said that he and others in the governor's office were "surprised that the Attorney General, contrary to her constitutional duty under the Commonwealth Attorneys Act, has decided not to defend a Pennsylvania statute lawfully enacted by the General Assembly, merely because of her personal beliefs."

That's just rhetorical eyewash from people who were outmaneuvered. Under state law, the Attorney General, as head of "an independent department," can refuse to enforce a law that he or she deems to be "not statutorily authorized or unconstitutional." And Kane's refusal is not exactly unprecedented; her counterparts in Illinois and California have refused to defend their states' gay marriage bans, and the Obama adminstration's legal team refused to defend the now-defunct Defense of Marriage Act.

(A quick aside: Kane's move yesterday could not have happened in New Jersey. Unlike in Pennsylvania, where the AG is an independently elective post - much to Corbett's dismay, because Kane has dogged him at every turn - New Jersey's top law-enforcement officer is appointed by the governor, thereby ensuring that the two are in sync on policy and politics.)

As for the Corbett counsel's complaint that Kane is defying "a Pennsylvania statute lawfully enacted by the General Assembly," that's a cinch to rebut: The US. Constitution trumps the will of the people. Because if the reverse were true, some states would still have duly-enacted laws banning racial integration. And some states would still have duly-enacted laws banning interracial marriage - as they did in 1967, when the U.S. Supreme Court swept away the last of those laws (including Delaware's), calling them "directly subversive of the principle of equality at the heart of the Fourteenth Amendment."

Kane implicitly referenced that Bill of Rights guarantee yesterday, but the essence of her political message to Corbett was simply this:

"Your move, sir. Better you than me."

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Meanwhile, in Washington, Harry Reid is vowing that this time he really, really, really, really does intend to go nuclear on the filibuster rules if the obstructionist Senate Republicans continue to sabotage President Obama's executive branch nominees.

Yeah, well. I'll believe it when I see it.

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Editor's note:  In an earlier version of this post, Pennsylvania Governor Tom Corbett was misidentified.  This has been corrected.