It's Election Day in Massachusetts!

Turnout is expected to be very low in Tuesday's special primary election for U.S. Senate, with the region still recovering from the Boston Marathon bombings and the campaign having attracted little attention even before the attack.

Polls close at 8 p.m. ET. We'll have results for you this evening on Post Politics. In the meantime, here's what we're watching:

Rep. Ed Markey (D). (Joshua Roberts/Reuters) Rep. Ed Markey (D). (Joshua Roberts/Reuters)

1. Ed Markey, frontrunner: Rep. Ed Markey has led the Democratic race from start to finish. With the party establishment squarely behind him, Markey's had a significant financial and organizational advantage over Rep. Stephen Lynch. The race heated up in the final week, with Lynch and Markey sparring over homeland security issues. But Markey never appeared to yield his advantage. Lynch might be able to hang in for a bit this evening, but look for Markey to secure the nomination.

2. Just how low will turnout be? Even before the Boston bombings, the campaign wasn't  drawing much attention. Boston Mayor Thomas Menino's retirement triggered an open race that upstaged the Senate race. Secretary of State William Galvin is predicting that turnout will be lower than in the 2009 special primaries. With only about 550,000 ballots expected to be cast on the Democratic side, efforts to get out the vote will be pressure-tested. While low turnout tends to favor the underdog, Markey has the Democratic activist wing of the party on his side, which could blunt strong support from Lynch loyalists.

3. South Boston: If Lynch is going to have a chance to spring an upset, he will need turnout in his South Boston base. The good news for Lynch: There is a state Senate special election in his district, which could boost turnout there. If his race is tight, keep an eye on the returns in Lynch's district. Markey will want to watch the numbers from his own suburban district, as well as from Western Massachusetts, viewed as the second-most liberal part of the state.

4. The Republican race: The GOP race has been competitive, with former Navy SEAL Gabriel Gomez and former U.S. attorney Mike Sullivan expected to compete for the nomination Tuesday night. Sullivan has been running as the most conservative candidate in the three-man field that also includes state Rep. Dan Winslow. Turnout on the Republican side is expected to be less than half the size of Democratic turnout, which means this could be an unpredictable evening. This much is certain: No matter who wins the GOP nod, the Democratic nominee will begin the general election campaign as a heavy favorite.