Voters in Colorado, New York, Oklahoma, South Carolina and Utah head to the polls today for primaries and primary runoffs.

Though no major Senate contests are on the ballot in these states, there are still plenty of interesting subplots. Here are five that are worth watching.

1. More incumbents going down?

Tuesday’s primaries could see yet more incumbents falling in newly drawn districts. The most likely victims would appear to be Reps. Charlie Rangel (D-N.Y.), Nydia Velazquez (D-N.Y.), Doug Lamborn (R-Colo.) and John Sullivan (R-Okla.).

Representative Charles B. Rangel in Washington, D.C., on June 20. (Marvin Joseph, The Washington Post)

Velazquez faces a challenge from New York City Councilman Erik Dilan, who is backed by Brooklyn Democratic power broker Vito Lopez in a district that took in large swaths of Brooklyn.

Lamborn, meanwhile, is an interesting case. While most primary challenges result from members not being sufficiently conservative or liberal (depending on the party), Lamborn is one of Congress’s most outspoken conservatives. Yet he still got a challenge from wealthy businessman Robert Blaha, who has spent $750,000 of his own money on the race. The best part of the primary: It has rekindled a bitter rivalry between Lamborn and his predecessor, former congressman Joel Hefley (R-Colo.), who recently called Lamborn a “knucklehead.”

Sullivan’s primary hasn’t been on the radar for long, but he faces and inspired challenge from tea party-backed political newcomer Jim Bridenstine. Sullivan acknowledged last week that “the only mistake I made was I ignored (Bridenstine) for too long.”

2. Hatch’s margin

One incumbent who is not likely to lose today is Sen. Orrin Hatch (R-Utah). The six-term incumbent is well on his way to a seventh term, according to late polling.

The win would be a triumph for Hatch, but a big win would be an even bigger triumph, especially given how big a target he was at the beginning of the cycle. Hatch has run a very good campaign, in contrast to Sen. Robert Bennett (R-Utah) in 2010 or Sen. Richard Lugar (R-Ind.) this year, and his margin is going to demonstrate that. (Of course, it didn’t hurt that Rep. Jason Chaffetz passed on the race.)

Also keep in mind: Lugar’s primary loss means Hatch will now be the dean of the Senate Republican caucus, which is no small thing.

3. Haley tests her political capital

There are two key open seat races today – one for retiring Rep. Dan Boren’s (D-Okla.) seat and one for the new 7th district in South Carolina.

Democrats have talked a bit about winning the conservative-learning new 7th, but their first recruit, state Rep. Ted Vick, succumbed to a drunk driving arrest, and now their second recruit, attorney Preston Brittain, appears as though he will lose a primary runoff to a woman who only recently resigned her seat in the Georgia House of Representatives, Gloria Tinubu. (More on that here.)

The real drama in this race is on the GOP side, where Gov. Nikki Haley (R) offered a late endorsement of Horry County Councilman Tom Rice over her 2010 gubernatorial opponent, former lieutenant governor Andre Bauer. The winner there is likely to be South Carolina’s new congressman.

In Oklahoma, the GOP primary could be headed for a runoff, with businessman Markwayne Mullin (GREAT name) and state Rep. George Faught favored to make it. On the Democratic side, the party hopes District Attorney Rob Wallace will make it to the general election, but this will be a tough seat to hold in a conservative area.

4. Rising stars in New York City

Rangel’s and Velazquez’s races aren’t the only big-time primaries in New York City. The race for retiring Rep. Ed Towns’s (D-N.Y.) seat has had every bit as much drama.

Towns faced two primary challengers before dropping out, and then he opted to endorse one of them, outspoken New York City Councilman Charles Barron. But national Democrats are wary of Barron, a former Black Panther, and they’ve got a rising star waiting in the wings in Assemblyman Hakeem Jeffries. The establishment, including Gov. Andrew Cuomo (D) and Sen. Charles Schumer (D-N.Y.), has rallied behind Jeffries in hopes of avoiding Barron in Congress.

And then there’s retiring Rep. Gary Ackerman’s (D-N.Y.) district, where state Assemblywoman Grace Meng, Assemblyman Rory Lancman and New York City Councilwoman Liz Crowley are facing off. Meng would be the state’s first Asian-American member of Congress (Ackerman’s district picks up a lot of Asian-American communities thanks to redistricting), while Crowley is the cousin of nearby Rep. Joe Crowley (D-N.Y.).

5. Upstate action

Upstate New York has proven one of the most important battlegrounds in the last three congressional elections, and this year should be no different. The two key primaries today are in districts held by Reps. Kathy Hochul (D) and Nan Hayworth (R), both which got tougher for the incumbents thanks to redistricting.

Hochul’s district is a top-tier GOP target, and two-time candidate David Bellavia and former Erie County Executive Chris Collins are battling for the right to face her. Give the edge to Collins.

Hayworth’s district features a Democratic primary matchup between Cortlandt Town Councilman Rich Becker and former White House aide Sean Patrick Maloney, who has the backing of former president Bill Clinton. Maloney is considered the bigger threat, but Hayworth’s new district, which went for President Obama in 2008, will be a target regardless.