Ed Kilgore at FiveThirtyEight has an analysis of the polls in the U.S. Senate race, and he says the Rand Paul phenomenon may not be all it’s cracked up to be, though Paul will likely win.

Anything other than a Rand Paul romp to victory tonight would be a major upset. Grayson has not led Paul in any public poll (other than one released by his own campaign) since last fall, and the most recent surveys, by PPP and the Republican firm Magellen Strategies, have both shown undecided voters breaking overwhelmingly for Paul. PPPhas Paul up 52/34, and Magellen shows him up 55/30. Paul’s only area of weakness, according to Magellen, is in the 5th congressional district, the “mountain Republican” area of eastern Kentucky where ideological conservatism, particularly as expressed in Paul’s hostility to federal programs benefitting Kentucky, has never been very strong. But Grayson’s likely margin in the 5th can’t offset landslide Paul wins in much of the rest of the state.

Media interpretations of the Republican Senate primary will be interesting. Given Paul’s parentage and quasi-libertarian views, the results will likely be taken as further evidence of an anti-incumbent, “insurgent” mood fed by unhappy independent voters. But a couple of cautionary notes on that meme: Kentucky has a closed primary system with a very early cutoff date for registration changes, so independents are quite literally not going to be a factor in Paul’s win or in the Democratic results, for that matter. Furthermore, there’s no incumbent in the race, and the actual incumbent, Jim Bunning, has endorsed Paul. And while Grayson’s impending loss is indeed humuliating for Mitch McConnell, it’s not at all clear the contest is some sort of referendum on his leadership. According to the latestPPP survey, Paul voters want McConnell to remain in his leadership post by a 58/22 margin.

In fact, PPP suggests that what’s feeding the Paul surge is a segment of self-conscious Republican voters who want their party to move ideologically to the right. According to PPP’s Tom Jensen:

32% of likely primary voters think the party is too liberal and Paul has a 71-21 advantage with them that accounts for almost his entire polling lead. With the other 68% of voters who don’t think the party is too liberal Paul is ahead only 45-41.Paul’s status as the candidate of “movement conservative” Republicans rather than tea-party independents or self-conscious libertarians, is buttressed by the endorsements he received from Sarah Palin, Jim DeMint and (in a reversal of an earlier Grayson endorsement) James Dobson.

In any event, you should take some of the hype you will hear tonight about Rand Paul’s “insurgency” with a grain of salt.