The quick economic case for V.P. Paul Ryan

Paul Ryan may be the only vice presidential short-lister who can save Mitt Romney from an economic crisis within the first month of his presidency. If that's not a good reason to put him on the ticket, what is?

The quick argument here: Assume Romney wins in November, and that the lame-duck Congress doesn't vote to raise the federal debt limit. (Both reasonable assumptions.) Now assume, as the Treasury Department estimates, that America hits the debt limit around the end of the year.

Treasury will start deploying "extraordinary measures" to buy time, probably a couple of months, before the government either defaults on some loans or misses scheduled payments to contractors or benefit recipients.

In that scenario, President Romney would take office with a ticking clock - maybe a month to raise the debt limit or impose the dramatic budget cuts and/or tax increases necessary to balance the budget immediately. The latter isn't likely - Romney's plan wouldn't balance the budget for eight years - so assume he needs to raise the limit.

Who will help him do it?

Ryan is his best hope.

Here's why: The math for another debt-limit increase is tough for a Republican president.

Democrats won't be in any mood to help out - especially since the increase would likely be tied to more budget cuts, and because Romney will be pushing for more tax cuts on top of it. So, with a few centrist Democratic exceptions, it's likely Romney will need to build a largely Republican coalition to raise the ceiling.

There's a not-small chunk of the House and Senate Republican caucuses who didn't vote for the last debt-limit deal. They're not likely to raise the ceiling just because Romney asked them to. To get their votes, he's going to need to link a debt-limit increase to a big batch of spending cuts - much bigger, probably, than the ones Romney has campaigned on. He'll need a credible salesman for those cuts. Enter Ryan.

The architect of the Ryan Budget is probably the only potential veep pick with the gravitas to walk into a room of skeptical House fiscal conservatives and say, trust us, these cuts are the real deal. Hold your nose and lift the ceiling.

If the Romney administration can't make that sale to its own party, then it will need to throw itself - and the economy, because a default would be a ticket to another recession - on the mercy of a just-vanquished opposition party. Recent history suggests that's not a great plan.