It’s primary day — again!

Voters in Maine, Nevada, North Dakota, South Carolina and Virginia are heading to the primary polls as we speak, while Arizona voters will pick a replacement for former congresswoman Gabrielle Giffords (D) and Arkansas voters will vote in a runoff.

With so many races on the ballot, here are five things to keep an eye on...

1. Arizona special election: What’s the margin?

Republicans are quietly expressing pessimism about the Giffords race, where GOP nominee Jesse Kelly has had some troubles trying to win a Republican-leaning district. But even if he loses, the margin matters.

As we mentioned this morning, we should not look to this race as a big indicator of what’s going to happen in the battle for the House. But if former Giffords aide Ron Barber (D) wins, it is a testament to Democrats’ continued success using Republicans’ desire to reform entitlement programs like Social Security and Medicare against them. If he wins big — as an automated poll Monday suggested — it’s an even bigger statement.

Indeed, Arizona was pretty much a perfect test case for this strategy, with an older electorate and Kelly’s past statements that he wanted to phase out the programs.

2. Maine Senate: Who gets to lose to Angus King?

Former governor and U.S. Senate hopeful Angus King (I) carries a box of signature-filled petitions to the Cross Building in Augusta on May 29 to get himself on the ballot. (AP Photo/Bangor Daily News, Troy R. Bennett)

On the Democratic side, former secretary of state Matt Dunlap and state Sen. Cynthia Dill are the favorites, while on the GOP side, a trio of Gov. Paul LePage’s (R) appointees — Secretary of State Charlie Summers, Attorney General Bill Schneider and state Treasurer Bruce Poliquin — and former state senator Rick Bennett are most likely to emerge.

The only public poll on the race has shown both primaries jumbled, with King leading all comers by 30-plus points in the general election.

The most interesting aspect of this race, though, continues to be whom, exactly, King would caucus with if and when he joins the Senate.

3. North Dakota and Virginia Senate: Tea party effect?

Former senator George Allen (R-Va.) and Rep. Rick Berg (R-N.D.), barring disaster, are going to win their party’s Senate nominations today.

In both cases, they face less well-funded opponents that have aligned with the tea party, and in each case, it will be interesting to see how much of the vote those opponents pull.

Allen is, of course, on a reclamation project after being booted from the Senate six years ago. He faces tea party activist Jamie Radtke and a social conservative favorite, state Del. Bob Marshall, with Radtke having spent the most on here campaign (about $700,000).

Berg faces perennial candidate Duane Sand, who has spent about $800,000 on his campaign and is well-known to North Dakota voters.

Both North Dakota and Virginia are shaping up as key open-seat takeover opportunities for the GOP — vital to the party’s effort to reclaim the Senate — and Allen’s and Berg’s relative strength will matter in those races.

4. Key House races: Who emerges?

There’s a smattering of notable House primaries spread across the six primary states tonight, but most of them are not top-tier races.

The one toss-up district holding its primary tonight — Nevada’s 3rd district — features no drama, with freshman Rep. Joe Heck (R-Nev.) set to face state Assembly Speaker John Oceguera (D).

The GOP will also pick a candidate in Nevada’s new 4th district, where state Senate Majority Leader Steven Horsford (D) should be favored against whoever emerges in the Democratic-leaning district (likely former Senate candidate Danny Tarkanian or businessman Dan Schwartz).

The GOP, meanwhile, will be favored to pick up the new district in South Carolina (the 7th), where there are crowded fields on both sides of the aisle and Democrats recently lost their top recruit after a drunk-driving arrest. Former lieutenant governor Andre Bauer and Horry County Council Chairman Tom Rice appear to have the inside track on making the GOP runoff there, but attorney Jay Jordan is a player too.

(Fun fact: A state legislator from Georgia, Gloria Tinubu, may make the runoff on the Democratic side, where attorney Preston Brittain is the establishment favorite.)

Democrats will also pick their nominees in some lower-tier races in Arkansas (where there are runoffs to face freshman Rep. Rick Crawford and in retiring Democrat Mike Ross’s district) and for Berg’s seat in North Dakota, where former state representative Pam Gulleson (D) will face one of two Republicans state public service commissioners, Brian Kalk or Kevin Cramer.

The GOP also holds out some hope against Rep. Mike Michaud (D-Maine), where state Sen. Kevin Raye is running but faces primary opposition tonight.

5. North Dakota: What happens with the property tax repeal?

North Dakota today could become the first state in the country — though it’s unlikely — to abolish the property tax, and the issue has both the right and left up in arms.

If voters opted to eliminate the tax, it would immediately create an $800 million hole in the state’s budget. Though the state is doing much better financially than a lot of others, that’s still a huge hole.

Which means that diverse entities including the Chamber of Commerce and public employee unions have joined forces to oppose the measure. And they seem to have fought it off, with 70 percent of North Dakotans opposing the repeal in a poll last week.

As the New York Times notes today, though, the idea is catching on in some other states, where similar ballot measures could be launched.