The Obamians are realistic about the fact that they need a significant share of the white working-class vote — and that Clinton is a better messenger for this group than the president is. My rule of thumb is that if Obama can hold Romney’s lead down to about 15 percent in the white working-class, he is almost certain to win.

Bill Clinton appeals to these voters (as Hillary Clinton did in the 2008 primaries).

To get a sense of where Clinton will be aiming his message, think of the long strip of Appalachian counties where Obama ran poorly, and places such as central and western Pennsylvania, and southern Ohio. If Clinton can tip even a half-dozen percentage points Obama’s way among these voters, he will have done his job.

Clinton also appeals to upper-middle-class voters who may not be wild about returning to the Clinton income tax rates but would love to have the Clinton economy and a balanced budget back. That’s where Clinton fits in well with the overall argument Obama is making. By associating his own policies with Obama’s, Clinton will be sending a message that happy days will be here again — eventually — if the country’s sticks with the incumbent and his preference for Clintonomics. Romney’s approach, as Clinton has already argued and will argue again, is nothing but Bushonomics “on steroids.” Obama has already picked up that line in his speeches.

And all the talk about Clinton as an empathetic, feel-your-pain kind of guy obscures a gift he has in common with Ronald Reagan. Clinton, as the Gipper did, knows how to make an argument. He knows how to explain things, how to describe what needs fixing and why his recipe for fixing things is the right one. In this case, he will be arguing for Obama’s recipe, explaining that it’s already made things better and, more important, that it will get the economy humming if we stay the course. (And yes, that’s an old Reagan slogan.)

 Underlining the fact that this convention will be about making an extended economic argument is the choice of Elizabeth Warren to speak right before Clinton. Warren, the Massachusetts Democrats’ Senate candidate and the scourge of the Wall Street high rollers, is a professor who really knows how to make a case. You can expect her to offer some reminders of the nature of the business Mitt Romney was in at Bain Capital. (And being linked to Clinton has to help Warren back home. Both Clintons are exceptionally popular in my native state.)

 My conservative colleague Jennifer Rubin argues that there is a risk that Clinton will “upstage a president who has lost his freshness” and “invite comparison between the two presidents' records and philosophies.” Clinton, Jen wrote, “is the anti-Obama.” You can be absolutely certain to hear this argument a lot from Republicans during the week of the Democratic Convention.

In truth, it is very hard to upstage the nominee at a convention. Barack Obama is no lightweight when it comes to giving strong performances when it matters. Indeed, I like the idea that Obama will be under extra pressure from Clinton’s presence to knock it out of the park in his acceptance speech. Obama, you may have noticed, is very competitive. As for Obama being the anti-Clinton, I think that’s just not true when it comes to policy — Obama, like Clinton, is a middle-of-the-road progressive and nothing like the lefty that conservatives claim he is. But my saying that is not as important as the fact that Clinton himself will be refuting that very argument throughout his speech. In a sense, Clinton is there to answer arguments of the sort that Jen made. And really: Is Mitt Romney in any way a natural choice for most of the voters who like Clinton? It’s hard to think of two people more different from each other.

 Obama’s lieutenants have signaled one other thing: Everything about their convention planning is strategic. Thus the importance of their choosing Mayor Julian Castro of San Antonio as the keynote speaker. Obama knows he needs to win huge majorities among Latinos. Right out of the box, this convention will send a signal to Latino voters that the president knows how important they are. And it will give the Democrats a leg up in the Spanish-language media.

 Will Romney’s high command be as strategic in its convention choices as Obama is being? One question to keep in mind: How much convention time does Romney have to give over to nailing down and activating his base? Some of that is necessary. Too much of it wastes a valuable opportunity.

Postscript: My views on this matter are not shaped by this video clip, but it seems right to disclose its existence.