The president’s agility on gay marriage and immigration is making his rival look stodgy and unprincipled.

Between the end of the primaries and the start of the conventions, presidential campaigns are message wars. Both sides test slogans and proposals while trying to frame their opponents in memorably unfavorable ways. In this phase, President Barack Obama has been the clear winner.

Obama has used the element of surprise, has taken risks that seem to be paying off, and has put his opponent on the defensive. He first seized the initiative in May when he endorsed gay marriage, changing his longstanding position. Even some on the right praised the president for acting on principle when the politics seemed against him.

But the politics of that issue may actually be on Obama’s side. Taking a moral stance on an issue of civil rights reanimated liberal voters who had drifted into disaffection, especially young voters who were crucial to his 2008 victory. Mitt Romney, who didn’t expect the move, found himself in an awkward position. With his radical Republican challengers dispatched, conservative positions on social issues were the last thing Romney wanted to emphasize. At a press conference, he called his own opposition to gay marriage “my preference” and declined to criticize Obama for changing his position or pandering to a Democratic special interest group. Romney’s response was essentially a tactical surrender that underscored the inevitably of liberal victory on the issue.