Before the Democratic convention began last week, John McCain had rallied to turn the presidential contest into a genuine horse race. His summer resurgence matched his come-from-behind victories in the GOP primary, indicating he's not a candidate you ever should count out.

That said, he has several factors working against him between now and November, and Republicans need to tackle them this week in St. Paul, Minn. Mr. McCain is back on the defensive in these last days in regard to the unpopular Bush presidency and is saddled with looking like Ed McMahon next to Barack Obama's Johnny Carson. Polls show most voters are zeroing in on Mr. Obama more than Mr. McCain.

Part of the problem is the ex-fighter pilot's inability to present a compelling narrative about where he wants to take America and how his life story uniquely qualifies him to lead the nation. The Democrats put on a powerful show in Denver, so Republicans need to start answering their own questions now.

For all of Mr. Obama's worries before Denver about Hillary Clinton dividing Democrats, Mr. McCain actually has the harder task of uniting his party.

Republicans are feuding among themselves about what happened with the Bush presidency. Mr. McCain lacks the enthusiasm Republicans felt for Mr. Bush when he emerged as the leader of a successor generation in 2000. And conservatives still distrust him for bucking them on immigration reform, taxes and the environment.

Early indications are that Sarah Palin could give his convention a jolt. The Alaska governor already has calmed down some of the conservative grumbling. His comparatively inexperienced running mate remains an unknown nationally, but she will rally conservatives on issues like abortion.

One surprise in Mr. McCain's unity quest is white evangelicals. Polls show they remain solidly behind him, even though he went to war against them in his 2000 campaign and can sound awkward when discussing religion.

Here's the tricky part, which undecided voters will study this week: At the same time Mr. McCain is rallying the GOP base, he has to keep alive enough of his maverick image to win voters closer to the political center. He has an opening with voters who worry about Mr. Obama's economics. Mr. McCain can win them on issues like lower taxes, but he could lose them if he steers too far right on cultural issues.

Add all this up, and Mr. McCain faces a dilemma. This convention will show how well he handles it.

Mr. McCain has claimed he doesn't understand economics, but his preference for keeping taxes low, especially those on investment capital, at least shows that someone in his campaign knows the tax code can be used to stimulate the economy.

Yet Republicans can't keep running simply as the party of tax cuts. Lower taxes alone won't push the economy forward, not when you consider the avalanche of debt headed toward future generations. The national debt is about $53 trillion – yes, with a "T" – if you add in the unfunded liabilities of Medicare and Social Security.

Billionaires Warren Buffett and Pete Peterson are promoting a film that details how this debt will overwhelm the economy if we don't do something about it now. Frankly, we're disappointed that Mr. McCain hasn't said more about this coming storm. He's taken many a tough vote in the Senate to correct entitlement programs and has an opening with the billionaires making our national debt a cause.

True, conventions may not be the best time to talk about coming storms. Still, Mr. McCain and GOP deficit hawks should remember Ross Perot credibly ran for president by lecturing about overspending. This week is a good time to revisit that.

Mr. McCain is undoubtedly the more experienced of the two nominees when it comes to world affairs. But experience alone won't win him the election if Mr. McCain uses this convention to simply gin up the Republican faithful by complaining about cut-and-run Democrats. Even if he wants to follow the lead of his neo-conservative/warrior advisers, the U.S. doesn't have the troop strength to hop from skirmish to skirmish.

Voters need to hear more from the Brent Scowcroft wing of Republicanism. Mr. Scowcroft, the former George H.W. Bush national security adviser, argues America must be more strategic in deploying its military strength.

Retreat? Hardly. Isolationists in both parties are dead wrong about that. And the terrorism threat is indeed the seminal challenge of this generation.

But Republicans will misread the public's mood if they believe America's ready to pick new fights all over the globe. As someone who reveres Theodore Roosevelt, Mr. McCain would do well to remember that he used the diplomatic touch to resolve crises as much as any president.

There's nothing Mr. McCain can do about being 72 years old, just as Mr. Obama can't change his lack of experience. Voters will have to take his age as a given and decide what to do with it.

That said, Mrs. Palin, 44, gives the Republican ticket a livelier feel. That could help them reach younger voters, particularly if Mr. McCain uses the debt issue to show how he intends to save them from economic calamity.

Another intangibles question is whether Mr. McCain can persuade voters he won't dissolve into rage in a crisis. Even Senate Republicans know him to be explosive.

To some extent, he has been easing up, using humor in town hall meetings, often aimed at himself. This week presents his best opportunity of the campaign to show that he's a guy Americans can trust in the hot seat.

The former Vietnam POW brings a heroic biography into the race. His career has been one of service to his country. But he and his party face a tough task after eight years of this Bush presidency. They need to show they are coming together with enough renewed energy and fresh ideas to lead the nation and the world for the next four years.