Barack Obama will leave Pennsylvania tomorrow in search of some small-town cred.

And he should not have to search for it alone.

The senator from Illinois could really use an endorsement from John Edwards, the Democratic contender who put small towns on the map–and carried a lot of them in Iowa and other states before folding a run for the Democratic presidential nomination that never got a break from the media or the party elites.

But, even if the former senator from North Carolina is playing Hamlet, Edwards-backer John Mellencamp has come through for Obama.

The Illinoisan is to be joined by the Indiana-rooted singer in Evansville, Indiana, on Tuesday night–as the results of the Pennsylvania primary are tabulated–for a rally that will acknowledge the Obama campaign’s awareness that it must put some serious effort into reconnecting with the rural and small-town voters who were once important players in the remarkable coalition that powered the senator’s surge.

For all the hopeful talk about how Obama has been forgiven for what sounded like an elitist jab at outstate voters, the fact is that the candidate and his aides know Obama hurt himself with his early-April remarks to a crowd of wealthy donors in San Francisco.

Yes, of course, Obama was trying to make an important–and valid–point when he told the Californians: “You go into some of these small towns in Pennsylvania, and like a lot of small towns in the Midwest, the jobs have been gone now for 25 years and nothing’s replaced them… and each successive administration has said that somehow these communities are gonna regenerate and they have not. So it’s not surprising then that they get bitter, they cling to guns or religion or antipathy to people who aren’t like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations.”

But Obama chose the wrong place and the wrong language to deliver the message–as the senator admitted publicly and bemoaned privately.

You don’t go to San Francisco and talk about how folks in small towns are “bitter” characters who “cling” to guns and religion.

And you sure as hell don’t perpetuate the elite fantasy that opposition to free-trade pacts should be seen “as a way to explain their frustrations.”

People — in small towns and big cities — who are critical of the North American Free Trade Agreement and permanent normalization of trade relations with China are not playing out some sort of “antipathy to people who aren’t like them.” They are reacting to the experience of seeing their jobs and their prospects disappear as factories close and service jobs are outsourced.

So what does John Mellencamp – on his own and as an extension of the Edwards campaign — have to do with this?

On the eve of the Iowa caucuses where it should be remembered that Edwards–not Hillary Clinton–finished second to Obama, the former senator from North Carolina finished his campaign with a “This Is Our Country” rally at the Val Air Ballroom in West Des Moines.

Edwards’ populist message–“Corporate greed is robbing our children of the promise of America. It is time for us to fight back”–was complemented that night by Mellencamp, whose song “Small Town” remains an anthem of many victims of that corporate greed. The song makes slight reference to economic concerns–-“My job is so small town/Provides little opportunity…”-–but it is not a litany of complaint. It is an expression of pride, a declaration that people who live in small towns cling to them even in tough times because they like the culture and character of their communities and because, as Mellencamp sings, they “cannot forget where it is that I come from.”

It is patently ridiculous to suggest that suburbanite Hillary Clinton or military-base John McCain understand small towns better than Barack Obama. They don’t. And they are at least as dismissive of the wisdom, the experiences and the legitimate sentiments of small-town Americans as the senator from Illinois seemed to be when he was talking to those folks in San Francisco.

But people expect more of Obama. The man who tells us that “words matter” was not expected to express himself so poorly. The candidate who has done such a good job of reaching out to rural America – winning states such as North Dakota and Nebraska by wide margins–is supposed to “get it.” No matter how Obama’s backers try to spin it, the suggestion that their candidate might not “get it” is going to disappoint people whose votes he may yet need in the primaries and he will definitely need in November.

How much he suffers will be determined not merely by Obama but by those who could, and arguably should, vouch for him. This is where Edwards and Mellencamp come in. They both have credibility not merely with Democrats, independents and perhaps even Republicans who live in small towns but with urban voters who understand what the song “Small Town” is all about. And they both know that Obama is an honorable player who may have made a mistake but whose background and campaign mark his as the only remaining serious contender for the presidency who might actually deliver for forgotten Americans.

Mellencamp, a longtime friend of the Clintons, has made his choice. He will stand with Obama on Tuesday night, at a point after the polls close in Pennsylvania when it will matter most.

Edwards should do the same–not merely for the sake of Barack Obama, but for his party.

Obama is almost certainly going to be the Democratic nominee. Now, the question is whether he is going to achieve that end as a strong contender for the presidency or as a candidate seriously wounded by his own mistakes and Clinton’s exploitation of them.

Mellencamp is sending an important signal, but Edwards could well decide the question. If he were to join Mellencamp at Obama’s side Tuesday night–of at some point in the near future–he could refocus the campaign and turn the whole “small-town” controversy into a source of strength for the likely Democratic nominee. By the same token, if Edwards remains on the sidelines, that failure will make the damage far more difficult to repair when, come the Fall, both Edwards and Mellencamp will be trying to elect a president who might actually do something for small-town America.