TOP OF THE BALLOT SUPER TUESDAY: It’s the first big primary day of 2010; Democrats are getting desperate in Hawaii; and Mitch McConnell tells us what we already knew – that he’s backing Trey Grayson.

It’s primary day!

Actual voting will take place today in three key states – Indiana, North Carolina and Ohio – so check out my rundown of what to watch for in today’s primaries.

The big question will be whether Cal Cunningham can force a runoff with North Carolina Secretary of State Elaine Marshall in that state’s Democratic Senate primary. If Marshall wins, the race against Sen. Richard Burr (R-N.C.) becomes less attractive to national Democrats. She needs 40 percent-plus-one to win outright.

The next biggest questions are how big former Sen. Dan Coats (R-Ind.) and Ohio Lt. Gov. Lee Fisher (D) win in their Senate primaries. Beyond that, we’re watching Reps. Dan Burton (R-Ind.) and Mark Souder (R-Ind.) to see if they struggle with primary challenges.

Keep an eye on it all tonight by checking the Ballot Box regularly.

Dem leaders make their Case

We’re getting into desperation time for Democrats in the Hawaii special election, with top Democratic officials now leaking a poll showing former Rep. Ed Case (D-Hawaii) in a much better position than state Senate President Colleen Hanabusa (D) in the three-way race. Ben Smith has the poll.

The takeaway here is that Democrats should unite behind Case in the name of keeping the seat. Both Democrats trail Honolulu City Councilman Charles Djou (R), but their combined vote total is 54 percent (34 percent Case, 20 percent Hanabusa), while Djou is at 36 percent.

This is where the vote-by-mail nature of the race is REALLY hurting Democrats. Even if Hanabusa can be pushed from the race eventually, she is already accumulating votes that Case will never be able to get back. And because there is no in-person voting on Election Day, the mail-in votes mean so much more.

All of that said, it’s hard to see a woman with the support of the state’s two senators simply stepping aside. And even if she doesn’t think she can win, she may have reason to stay in the race. By Djou winning the seat, she improves her chances of grabbing the seat back in November, after Democrats hold a proper primary. That process would favor the more left-leaning Hanabusa.

McConnell endorses Grayson

One of the worst-kept secrets on the 2010 campaign trail has gone official: Senate Minority Leader Mitch McConnell (R-Ky.) is backing Trey Grayson in this month’s Kentucky GOP Senate primary.

Grayson’s campaign announced McConnell’s endorsement this morning, with the state’s senior senator also appearing in a new TV ad for the Kentucky Secretary of State.

Any illusions that McConnell and the GOP leadership are neutral in this race are now gone. Grayson is seeking a bump – any bump – and making McConnell’s support official appears to be the latest effort.

The fact that McConnell is the state’s other GOP senator may help Grayson in his race against the frontrunning Rand Paul, but the fact that McConnell is a GOP leader may only reinforce the insider-versus-outsider plot that exists in this primary.

Other updates

-Rep. Mike McMahon (D-N.Y.) has released a poll showing him leading both of his potential GOP opponents by around 30 points.

-Maricopa County Sheriff Joe Arpaio announced Monday that he would not seek the GOP nomination for governor of Arizona. That leaves Gov. Jan Brewer and state Treasurer Dean Martin as the GOP frontrunners.

-Todd Palin is doing a fundraiser for Sen. Lisa Murkowski’s (R-Alaska) primary challenger.