As punishing on voters as long presidential campaigns can be, at least they usually provide a chance to see a candidate forced to confront a crisis.

Witness Barack Obama as he seeks to extinguish the firestorm over his former pastor, the Rev. Jeremiah Wright Jr.

I thought Obama gave an impressive speech in March as he tried to defuse controversies swirling about the minister, seeking to respect a long-time relationship with the man but decrying incendiary snippets of sermons that had made it to TV and calling for a thoughtful national dialogue about race.

Of course, it’s hard to have a meaningful dialogue when other candidates don’t constructively join in and voters prefer silence to admitting their prejudices.

Obama’s March speech proved to be not enough. Now folks ask why he waited so long, until this week, to break so dramatically and finally from Mr. Wright.

But until the minister’s recent high-profile public appearances, notably a ranting televised in-your-face destructive presentation Monday at the National Press Club, he had become only background music. Suddenly he exploded again on the national scene, this time full force, not only making ridiculous, racially charged comments but also suggesting that Obama’s previous distancing himself from him was the action of a phony politician.

Now a wounded Obama had to, and did, respond angrily and decisively. With luck, he can move on from here, perhaps even win points for standing up to a militant black voice. It has been a severe distraction from his efforts to woo white working-class voters in Democratic primaries next Tuesday in North Carolina and especially Indiana, and to impress superdelegates everywhere. If Hillary Clinton beats him in Indiana, where his lead in the polls has virtually disappeared, it will rock his candidacy.

It’s interesting to see both aspirants undermined by someone who has been close to them — in Clinton’s case, her husband Bill. But it’s been several days since the former president last strayed off message and said something dumb and offended black voters or others, and Senator Clinton is playing a hot hand, homing in on a message of jobs, jobs, jobs.

In her appeal to financially pinched voters, she, like Republican John McCain, is willing to tout the empty idea of suspending the 18-cent-a-gallon federal gasoline tax over the summer.

It sounds great but at best would save motorists only a few dollars. Indeed, lower prices might increase consumption and push prices up again. I don’t think the nation ever will bring this problem under control until a president and a Congress have the will to buck the public’s love affair with big cars and force manufacturers to make smaller vehicles with more use of alternative energy, and until there is a massive expansion of public transportation. Rhode Island, for example, should be doing much more with commuter trains and light rail (i.e. trolleys).

In the quest for Democratic votes, I applaud Obama for not joining Clinton’s call to suspend the gasoline tax; I admire him for it, but it likely will cost him votes from people who are hurting and looking for a quick fix.

So Obama will take it on the chin in those quarters, as he has taken it on the chin on the Wright issue and some other flaps. He has lost significant luster. You don’t hear talk any more that he’s too good to be true. This can be fortunate for him: If he manages to win, there’ll be less tendency to expect him to work miracles.

M. Charles Bakst is The Journal’s political columnist.

mbakst@projo.com