Today is a major primary day, with Pennsylvania, Kentucky and Arkansas holding Senate primaries, and Oregon a gubernatorial primary.  I’ll deal with these by poll closing times: Kentucky at 6 p.m. and 7 p.m. EDT; Pennsylvania at 8 p.m. EDT; Arkansas at 8:30 p.m. EDT; and Oregon at 10 p.m. EDT.

In Kentucky, it looks like Rand Paul is very likely to win the GOP Senate nomination, beating Secretary of State Trey Grayson, the fair-hair child of the Bluegrass Republican establishment, and particularly of Senate Minority Leader Mitch McConnell.  Paul has been leading Grayson steadily in every recent poll, and the latest, from Magellan Strategies, shows Paul pulling away with a 55/30 lead.  Another recent poll, from PPP, shows that fully one-third of Kentucky Republicans think their party is “too liberal,” and it’s these voters who are fueling Paul’s surge.  Even though this is a closed primary and Paul is in many respects a conventional if extreme conservative, as indicated by the endorsements he received from Sarah Palin, Jim DeMint and James Dobson, expect to hear a lot of “Tea Party Insurgency!” hype when the results come in tonight.  Hype aside, Paul’s non-interventionist views on foreign policy, which are similar to his father’s, are unusual for a Republican politician, and it’s quite interesting that Grayson’s attacks on them didn’t gain much traction.

The Democratic Senate primary will likely provide the only real drama in Kentucky tonight, with polls indicating a close race between Lt. Gov. Dan Mongiardo and Attorney General Jack Conway.  Though Conway has been endorsed by MoveOn.org, the contest hasn’t been particularly ideological; both candidates oppose cap-and-trade legislation, and while Mongiardo has said he would have voted against health reform in the Senate, it’s because the bill “didn’t go far enough.”  Conway has had a significant financial edge, and seems to have some late momentum, but the geographical turnout patterns —Mongiardo is from Eastern Kentucky, while Conway is from Louisville — will probably determine the result.  Both candidates trail Paul in general election polls by a considerable margin.

Pennsylvania’s Democratic Senate primary is a genuine barn-burner, with party-switching incumbent Arlen Specter trying to hold off a late surge by Rep. Joe Sestak.  Every poll in the last week has shown Specter losing his relatively large lead over Sestak, as the challenger benefits both from the support of progressives who dislike Specter’s partisan background and from moderate-to-conservative Democrats who don’t like his social liberalism or his current pattern of staunch support for the Obama administration.  It is universally conceded that the race will all come down to turnout, with Specter—who is being backed not only by the Obama administration, the DSCC, and Gov. Ed Rendell’s organization, but also by most major unions—counting on a large turnout from Philadelphia, where he has a huge lead among African-Americans.  Both candidates have trailed Republican Pat Toomey in most polls, though Sestak’s general election numbers have been significantly improving recently.

The other Pennsylvania race drawing national attention has been the special election to replace the late Rep. John Murtha.  It’s the classic Western PA white-working-class district: it’s been represented by Democrats since the New Deal, and was carried by both Al Gore and John Kerry, but not by Barack Obama.  Unsurprisingly, the most recent public polling, by PPP, showed a dead heat between Democrat Mark Critz and Republican Tim Burns.  A Democratic hold in this seat, widely expected to go Republican when Murtha died, would provide a real boost to Democratic morale.

In Arkansas, the marquee contest matches Lt. Gov. Bill Halter against Sen. Blanche Lincoln, but the race has almost been overshadowed by national interests.  Halter has strong backing from a variety of unions who are enraged by Lincoln’s flip-flop on the Employee Free Choice Act, while the incumbent, who chairs the Senate Agriculture Committee, has received massive backing from the agribusiness and financial industries. Millions are being spent on both sides on “independent” ads attacking one candidate or the other.  Lincoln is also being supported by the president and by former president Clinton.

Polls have consistently shown Lincoln leading Halter, but with less than 50 percent of the vote. If Lincoln or Halter is unable to win a majority of the votes, they will faceoff in a runoff election as required in Arkansas. There is a sizable undecided vote among African-Americans, who lean towards Halter, and Lincoln’s campaign has been running Obama and Clinton radio ads aimed at African-Americans.  Regional turnout will also be a big factor, with Lincoln expected to do well in the Delta region she used to represent in the House, and Halter expected to do well in Little Rock.  The contest could well serve as a lab experiment on the ancient proposition that undecided voters invariably turn against incumbents; if Lincoln gets a decent share of the undecided vote, she should win.

The Republican Senate primary is a low-profile affair with eight candidates, and it’s been generally assumed that Rep. John Boozman will win, probably without a runoff.  Boozman will be helped by geography: he represents northwest Arkansas, a heavily Republican area where turnout will be boosted by a highly competitive primary to choose his replacement in the House.  But two other candidates in the field, state senator Gilbert Baker, who is from central Arkansas, and former statewide candidate Jim Holt, a fiery Tea Party-style conservative who shares Boozman’s geographical base, could get enough support to force him into a runoff, particularly if voters respond to attacks on Boozman for supporting TARP.

Every poll taken this cycle has shown both Lincoln and Halter trailing every named Republican in general election trial heats.  The big question is whether Arkansas’ strong tradition of voting Democratic downballot even when support for the national party is weak is finally expiring as it has in other parts of the Deep South.

In Oregon, limited polling predicts that former Gov. John Kitzhaber will easily win the Democratic gubernatorial nomination over former Secretary of State Bill Bradbury.  His Republican opponent is expected to be former Portland Trail Blazer Chris Dudley, but don’t be surprised if conservative Allen Alley pulls an upset, as one late poll suggests is possible.

Finally, in non-primary political news, a major brouhaha has broken out in Connecticut, where Democratic Attorney General Richard Blumenthal, who was the heavy favorite to hold onto Chris Dodd’s Senate seat in November, was the subject of a big New York Times story (fed by one of his Republican rivals) revealing that he has on at least one occasion referred to himself as a veteran of the Vietnam War. It turns out that he’s not; he served in the Marine Reserves during that war, but never deployed.  At the moment, the DSCC is standing by Blumenthal, but Connecticut Democrats do have the option of choosing another candidate in their state convention, which will be held this weekend.

Ed Kilgore’s PPI Political Memo runs every Tuesday and Friday.