Washington (CNN) The national debate over gun control has thrown a new dynamic into this year's top Senate races.

For the five Democrats defending seats in states President Donald Trump won in 2016 by double-digits, the issue is complicated: Their national party and donors want gun restrictions, but the right-of-center, exurban and rural voters they'll need to win have historically opposed tighter gun laws. They'll have to decide how far they can go, and how they can sell it.

For some Republicans, particularly Florida Gov. Rick Scott, it's a different problem: They'll be accused of ignoring opportunities to act on gun violence before the shooting in Parkland, Florida.

As we wait to see how the gun debate evolves in statehouses and on Capitol Hill, here's our March edition of the 10 Senate seats most likely to switch parties in November.

Remember: The current balance of power in the Senate is 51 Republicans, 49 Democrats (and independents who caucus with them). That means Democrats need a net gain of two seats to take control of the chamber. That's a tough task on a map where Democrats are defending 26 seats and Republicans just have to hold eight.

1. Nevada

Incumbent: Republican Sen. Dean Heller

Primary date: June 12

Heller tops this list for two reasons: He's the only Republican up for re-election in a state Hillary Clinton won in 2016, and unlike the split fields we see in other states, he has dangerous one-on-one matchups in both the primary (against Danny Tarkanian) and the general election (against Rep. Jacky Rosen).

The good news for Heller: President Donald Trump wants to help him. Trump told Republican National Committee members he'll go to Nevada to campaign for Heller ahead of the primary. (And if Trump forgets that promise, the fact that Tarkanian used Ivanka Trump against Heller will probably serve as a strong reminder.)

The bad news: Cozying up to Trump is a problem in a general election.

2. Arizona

Incumbent: Open seat (Republican Sen. Jeff Flake is retiring)

Primary date: August 28

In a year of Republican primaries all over the map, this one has the makings to be the nation's most chaotic.

Rep. Martha McSally spent much of the last month backing away from her 2016 criticism of Trump. Former state Sen. Kelli Ward was in Washington for CPAC courting major donors and organizations for a well-financed brawl. And former Maricopa County sheriff Joe Arpaio is a wild card who could spoil the entire race for Republicans if he wins the primary.

With the primary still months away, Democratic Rep. Kyrsten Sinema is watching and waiting.

Flake, meanwhile, is off to New Hampshire for an event later this month, kicking up 2020 presidential speculation.

3. Missouri

Incumbent: Democratic Sen. Claire McCaskill

Primary date: August 7

Republican attorney general Josh Hawley has played the scandal surrounding indicted Gov. Eric Greitens carefully, breaking with the Missouri GOP in calling for an investigation and tweeting that there is "no place for party or partisanship."

A felony indictment by a grand jury is a serious matter. There is no place for party or partisanship. The criminal justice system must be allowed to work. I am confident the House's investigation will be thorough and swift, and will proceed without regard to party. — AG Josh Hawley (@AGJoshHawley) February 23, 2018

Still, Greitens' seemingly inevitable downfall is bad for the party's brand. Navigating those choppy waters -- ideally as quickly as possible -- is important for Hawley's Senate prospects in a state Trump won by 19 points in 2016.

4. Indiana

Incumbent: Democratic Sen. Joe Donnelly

Primary date: May 8

In the three-way Republican primary between Reps. Todd Rokita and Luke Messer and former state Rep. Mike Braun, it's Rokita who wields the sharpest knife.

His opening line in their first debate got at both Braun's past participation in Democratic primaries and questions surrounding Messer's residency. "Mike, welcome to the Republican Party," Rokita said. "Luke, welcome back to Indiana."

Rokita's all-base, all-the-time strategy was on vivid display in his first TV ad:

5. West Virginia

Incumbent: Democratic Sen. Joe Manchin

Primary date: May 8

Manchin tried an odd idea last month: He urged other senators to sign a pledge not to campaign against each other.

It seemed like a self-serving proposal by a former governor who, while in that job, was chairman of the Democratic Governors Association, an organization with the sole job of defeating Republican governors.

Even if senators stay out of it, others are willing to wade in. Wisconsin Gov. Scott Walker endorsed attorney general Patrick Morrisey, who along with Rep. Evan Jenkins and coal CEO Don Blankenship are running to oppose Manchin.

6. North Dakota

Incumbent: Democratic Sen. Heidi Heitkamp

Primary date: June 12

Republicans got good news when Rep. Kevin Cramer changed his mind and decided he'd run against Heitkamp after all.

The cherry on top: There won't be a GOP primary. State Sen. Tom Campbell, who was also in the race, is instead running for Cramer's House seat.

Heitkamp will benefit from footage of Trump extending a handshake and calling her a "good woman" on stage at a September event. But there are good reasons Republicans consider this a top target: Trump won the state by 36 points in 2016. And Heitkamp won her seat by less than a point in 2012.

Heitkamp is still well-funded and hasn't had to cast many tough votes (with tax reform being a possible exception), and there remain questions about Cramer's strength as a candidate. But this race looks better for Republicans now than it did a month ago.

7. Montana

Incumbent: Democratic Sen. Jon Tester

Primary date: June 5

Last in a string of five straight Democratic-held seats in states Trump won by double digits, Tester is watching and waiting to see how the GOP primary develops.

State auditor Matt Rosendale, the other Senate candidate with a flat-top, appears to be the Republican front-runner, with businessman Troy Downing, former judge Russell Fagg and state Sen. Al Olszewski are also in the race.

8. Wisconsin

Incumbent: Democratic Sen. Tammy Baldwin

Primary date: August 14

Many families dislike the political life. But rarely do you see the parents of a candidate -- Republican businessman Kevin Nicholson -- give the maximum possible donations to his Democratic opponent , Baldwin.

Nicholson has challenged state Sen. Leah Vukmir to six debates in a primary that is still developing. Businessman Eric Hovde is also exploring a run.

The first debate is set for March 28 hosted by WTMJ-AM and being broadcast on the radio.

9. Ohio

Incumbent: Democratic Sen. Sherrod Brown

Primary date: May 8

Here's the counterintuitive case for Republicans having a shot here:

When state treasurer Josh Mandel dropped out, the assumption was that Brown probably had this race in the bag. But the truth about Mandel was that Republicans never believed he'd win. They'd already seen Brown beat him once, in their 2012 head-to-head.

At least Rep. Jim Renacci, the front-runner for the nomination, gives the GOP a bit of a clean slate. He's capable of self-funding at least partially in an expensive state, too.

As Ohio drifts rightward, it's possible this one will be harder for Democrats to put away than they'd like.

10. Florida

Incumbent: Democratic Sen. Bill Nelson

Primary date: August 28

In the wake of the Parkland shooting, Nelson is showing that he's ready for a fight against Gov. Rick Scott, the Republican who is widely expected to announce a Senate run in the near future.

In a CNN town hall on guns, Nelson linked Scott's inaction in the wake of the Pulse nightclub shooting in Orlando to the Parkland shooting.

"Two years ago, when 49 lives were taken in the Pulse nightclub, and nothing was done -- not in Washington, not in Tallahassee, not one thing offered by the administration in Tallahassee," he said. "And here we are, going through this again. And it's going to unfortunately very possibly continue unless we get some common-sense laws on the books."