What makes a vote 'the deciding vote'?

What's worse than voting for a controversial bill? Being "the deciding vote" on a controversial bill. And not surprisingly, it's been a theme of several campaign commercials we've rated this year.

• PolitiFact Wisconsin looked at campaign literature from Republican Senate candidate Ron Johnson. It claimed that his Democratic opponent, Sen. Russ Feingold, "cast the deciding vote" for the health care bill in 2009. The claim earned a rating of Barely True.

• PolitiFact Oregon checked a claim in an e-mail by Republican challenger Scott Bruun. Bruun charged that Democratic Rep. Kurt Schrader "cast the deciding vote that failed to extend tax cuts for Oregon"s middle-class families and small businesses." The claimed earned a rating of False.

Now, we rate an ad by the National Republican Senatorial Committee in the Colorado Senate contest between incumbent Democrat Michael Bennet and GOP nominee Ken Buck. The ad attacked Bennet's role in helping pass two Democratic-sponsored bills, the economic stimulus and the health care overhaul.

"One vote makes a difference," the narrator says. "Michael Bennet cast the deciding vote for Obama's stimulus that wasted billions, added to the debt and didn't create the jobs they promised. Bennet cast the deciding vote to allow passage of the trillion-dollar health care bill that slashed Medicare, hurting seniors. Bennet's vote was the key to billions in job-killing taxes, too. Michael Bennet: He's been their vote, not Colorado's."

Both measures passed with exactly the required 60 votes, so Bennet's vote was certainly crucial. But we concluded that any of those 60 votes would have been a deciding vote on those measures -- and that Bennet had done nothing (such as holding his support until the last moment) that would justify singling him out. We rated it Barely True.