But their most prominent and important one is this: Collins is a champion of compromise. She works well with Democrats. She's great at crafting bipartisan solutions.
We're likely to hear this argument--call it the "Collins plays nice" thesis--ad nauseam between now and election day. And to be fair, it does have some truth to it.
Of course, one wonders where the junior senator's bipartisan spirit was when she parted ways with Sen. Snowe to vote for the unaffordable 2003 Bush tax cuts, ramrodded through Congress with the aid of Vice President Dick Cheney's tie-breaking vote.
And to be sure, there's a big difference between shepherding meaningful, big-ticket legislation through Congress and backing token measures designed to massage problems rather than solve them--Collins' drop-in-the-bucket plan to narrowly trim Iraq spending comes to mind.
Still, the core idea--that the junior senator gets along with Democrats and has little trouble working with them--seems to be basically true.
But here's where things break down: The notion that working well with others, across party lines, should count as some sort of re-election credential is ridiculous. It's beyond silly.
Because being able to compromise is a basic job requirement in the Senate. As long as the filibuster exists, it's the only way things get done.
Sen. John McCain (R-AZ) has worked extensively with Democrats. And Sen. Barack Obama (D-IL) has done the same with Republicans. The same is true of polar opposites Sen. Tom Coburn (R-OK) and Sen. Edward Kennedy (D-MA).
That doesn't make them moderates or centrists. And it's not an important selling point for their re-election. Instead, it speaks to each senator's recognition that he was sent to Washington, D.C. with a job to do. And that he'll almost always need bipartisan support to do it.
So let's get real: The idea that Sen. Collins is unique--or uniquely-adept--at crossing the aisle to get things done is nonsense.
She's not better at it. She just talks about it more than anyone else.