So here we go. Yes, even though Christie is more popular than ever as a Republican in "blue" New Jersey - a Rutgers-Eagleton poll two weeks ago had him at 50 percent favorability, the highest of his term - he cannot deliver New Jersey for Romney. A Romney-Christie ticket would still get handily defeated by Obama-Biden, polls show.
But what if we cross the Delaware River into Bucks County and around to Montgomery, Chester and Delaware Counties? The fabled swing counties that determine how Pennsylvania votes for senators, governors, presidents. If Pennsylvania turns out to be a swing state, those counties could determine the next president.
Some say the Romney-Obama showdown hinges on nine states: Colorado, Florida, Iowa, Nevada, New Hampshire, Ohio, Pennsylvania, Virginia, and Wisconsin. That has helped propel politicians in most of those states to the top tier of GOP vice presidential possibilities: Florida Sen. Marco Rubio, Wisconsin Rep. Paul Ryan, Virginia Gov. Bob McDonnell, and New Hampshire Sen. Kelly Ayotte.
Christie now seems to be atop the second tier. Would that change if Romney thought Christie could help him win Pennsylvania?
Consider, first, name recognition. Though New York abuts New Jersey, New Yorkers are too concerned with themselves to worry about someone else's politicians. So Christie might be better known in Pennsylvania than any other state outside his own.
Plus, his mug turns up on Philadelphia-area TV. With a look and speaking style unusual for politicians, this guy gets news coverage galore - particularlly given the relatively low-wattage personalities of Pennsylvania politicians in the post-Ed Rendell era.
He even gets face time during commercial breaks. A pro-Christie group has paid for several ads in this market.
Meanwhile, untold scores from Philadelphia's Pennsylvania suburbs migrate to the Jersey Shore each summer, where they hear talk of Christie at the deli - or at least see the governor's name on the sign for the Garden State Parkway.
And there's even precedent: In 2010, a GOP congressional candidate in that same four-county zone brought Christie in to campaign for him. And Pat Meehan won.
No public polls have tested an Obama-Biden vs. Romney-Christie matchup in Pennsylvania. But the mind boggles at the possibilities of a debate: Biden, the say-anything kid from Scranton, and Christie, the say-anything kid with the wife from Paoli!
"I think Christie would give Romney the best bump in Pennsylvania of any of the popular vice presidential options - but that bump would be very small," said Christopher Borick, a political scientist at Muhlenberg College.
"Christie's efforts at fiscal reform, more moderate stances on social issues, and familiarity make him a comfortable fit for voters in the very important Philadelphia suburbs, but I'm skeptical that he would swing a significant number of voters."
G. Terry Madonna, director of the Franklin and Marshall College Poll, said that instead of geography, Romney should make sure his pick does no harm (no Sarah Palin), evokes credibility in voters' eyes as a possible president, and can be an attack dog on the campaign trail if needed.
That Christie doesn't stress his pro-life views would be helpful in the four Pennsylvania counties, Madonna said. That he is "loquacious, controversial," could be a problem, he said.
Obama now leads by 23 points in Southeastern Pennsylvania, according to a Franklin and Marshall poll. That would be a tough gap to close for Romney-Christie - but to win the state's 20 electoral votes, they might not have to close the gap entirely.
Sabato said Christie backers may be making that very argument to the Romney camp. "Pennsylvania has suckered in a lot of Republicans through the years," he said, recalling how Bush adviser Karl Rove thought Bush could win there in 2000. "For all I know, there's some naive person in the Romney campaign whose biting on the line and getting ready to be reeled in."
Still, the state hasn't gone Republican for president since 1988. And the last V.P. from New Jersey was Garret A. Hobart, a Republican who ran with William McKinley in 1896.
They won Pennsylvania that year.
And, incidentally, they won each of the four counties around Philadelphia.
Contact Matt Katz at 609-217-8355, email@example.com, or follow on Twitter @mattkatz00. Read his blog, "Christie Chronicles," at www.philly.com/