Rob Portman’s position reversal to support gay marriage creates one of the biggest political and cultural Rorschach tests of the year for the in-search-of-its-new-self Republican Party. (see Roll Call news story.)

From the floor of the CPAC convention to the bar at the Capitol Hill Club to the offices of the Log Cabin Republicans, an enormous range of questions are being pondered now that the Ohio senator has revealed — on CNN last night and in the Columbus Dispatch this morning — that he changed his mind about one of the defining social issues of our time because one of his sons told him he is gay.

The story is undeniably important because it makes Portman, already one of the most serious and respected voices in the party on fiscal policy, the only current GOP senator publicly embrace same-sex marriage. But why?

Was his decision to renounce a career’s worth of votes against equality for gay couples a straightforward matter of a parent doing the best thing he could to support his child? Was it a calculated decision to clear his conscience during a somewhat slow period in his career, after just one turn in the national limelight and with plenty of time before he might seek to return there?

Was it an attempt to get on the right side of history for the sake of his own political future, or to push his fellow Republicans to get there before it’s too late?

Did he wait so long — the younger Portman came out to his parents two years ago, when he was a 19-year-old freshman at Yale — because père wanted to protect fils’s privacy as long as the boy wanted? Because it took him this long to square his own socially conservative views with the realities of his family life? Because he wanted to see how his vice presidential prospects last year would play out? Because doing so now might help leverage public sentiment at the most opportune moment — 10 days before the Supreme Court hears arguments about whether restricting marriage for gay couples is constitutional?

There’s evidence to support “yes” answers to all of those questions, much of it in what Portman himself is saying. Politicians, like parents, are at their most effective when they’ve thought through all the angles and make a bold move. At first blush today, Portman’s news appears to bring him and his party three-dimensional benefits.