CNN’s Political Ticker reports that with Ted Kennedy apparently unavailable for a Senate vote tomorrow, Harry Reid is trying to line up one more Republican to vote for the Democrat spending bill. The concern is that without Kennedy, the bill has only the minimum number of votes required to pass: 60. And the three GOP supporters had made clear that their support was conditional on there being 61 votes — so none could be described as the decisive vote that passed the package.

According to Roll Call (subscription required), Reid has a backup plan in case he can’t get another Republican:

One senior Senate Democratic source said Reid was exploring the idea of having Kennedy’s absent vote in favor of the bill paired with a Republican who would otherwise vote against the bill. Though paired votes are not counted in the total, they do remain a part of the Congressional record, which could give the GOP centrists a way to prove they were not the decisive vote on the bill.

Specter is regarded as the most vulnerable to political attacks for his support of the stimulus measure because he is planning to run for re-election in 2010 and could face a primary challenge from the right.

‘Vote pairing’ is not unusual in cases where a Senator can’t make a vote. He or she finds a Senator on the opposite side of the issue who also could not make the vote. The two agree to ‘pair’ their missed votes – to demonstrate that they in fact, cancelled out. So if Kennedy is ultimately unable to vote, he would try to identify a Republican opponent of the bill to enter into a ‘pair.’

There are a few problems with this idea. First, what opponent of the bill would agree? Even if a Republican is for some reason unable to vote, few would give Reid this breathing room. Second, even if a pair is agreed upon, would you want to explain it to Pennsylvania voters if you were Arlen Specter? I doubt the claim will get very far.

And third, going forward with 60 votes doesn’t just hang Specter, Collins, and Snowe out to dry, it does the same for every red and purple state Democrat. Michael Bennett, Kent Conrad, Blanche Lincoln, Claire McCaskill, Ben Nelson, Mark Pryor, Jon Tester, Jim Webb — you can go down the list of Democrats in less-than-safe seats, who might be nervous about being described as ‘the decisive vote’ for the plan. Expect Reid to run into trouble if Kennedy is unavailable and he can’t get another Republican to cross over.