Sometimes, it feels as if Senate Republicans are playing whack-a-mole in their attempt to keep control of the Senate in November.

They're now favored to hold the Senate, according to The Fix's 2016 Senate race ratings. That's thanks in large part to candidates in Ohio and Florida pulling ahead of their Democratic challengers, sparing their party from having to dump millions in these expensive states.

But while Republicans probably feel much feel better about their chances in Ohio and Florida than they did a few months ago, it's safe to say they feel worse about their chances in three red-leaning states: Indiana, Missouri and North Carolina.

To take back control of the Senate they lost in 2014, Democrats need to knock off four Republicans (or five if Donald Trump wins the White House and Indiana Gov. Mike Pence (R) is the Senate's tiebreaker). Increasingly, it looks as if that battle will be playing out in these three states:

Indiana: The surprise battleground state

The basics: Indiana's open Senate seat (Sen. Daniel Coats (R) is retiring) wasn't on most people's radar until recently. The state had voted for the Republican presidential candidate every election for the past three decades except once, in 2008. This year, it's expected to go for Trump. Republicans were excited for their chosen nominee, Rep. Todd C. Young (R).

Then Coats's rival, former senator and governor Evan Bayh (D), changed all that. He jumped into the race in July, apparently convinced by arguments that Trump's unpopularity, along with Bayh's $10 million leftover war chest was a winning combination.

We now have the race as a toss-up, and third most likely to flip parties.

Where the race stands now: Republicans aren't giving up their Indiana Senate seat without a fight. GOP outside groups like the Chamber of Commerce and the Koch brothers have already spent $10 million attacking Bayh (He's a lobbyist! He doesn't even really live in the state!). Bayh's once 20-plus point lead (we can't overemphasize how well-known he is in the state) has closed to an average 5.5-point edge, according to RealClearPolitics.

What this race will probably come down to: Bayh is still infinitely better known than his opponent and has more money (even though he's already spent a good chunk of it) -- so the outcome will hinge on whether GOP attacks on Bayh stick.

Missouri: The generational battleground

The basics: This race always had the potential to be competitive in a wave year for Democrats. But even absent any indication of a wave, it's suddenly looking competitive.

Sen. Roy Blunt (R) has represented Missouri in Congress for almost two decades, and he's trying to fend off a 35-year-old military veteran.

Missouri Secretary of State Jason Kander is one of the Democrats' prized recruits this cycle, and so far he's running a smart campaign. He came out against the Iran deal. He ran one of the best TV ads of the election so far. To blunt Blunt's attacks on his gun record, Kander assembled an AR-15 assault rifle while blindfolded, talked about his preference for background checks and dared Blunt to do the same.

Kander is basically running as a Republican, and that's exactly what he needs to do in Missouri, a state that has been trending red at the federal level. Meanwhile, Democrats are trying to pin Blunt's family lobbying ties. (His wife and three of his children are lobbyists. One of his sons runs his campaign.) Outside groups are pouring in millions on both sides.

Where the race stands now: The average of recent RealClearPolitics shows Blunt up by 3.4 points. The Fix has the race as leaning Republican and 10th most likely to flip parties this cycle.

What the race will come down to: Whether Kander can successfully convince Missouri voters that they need a change agent in Washington.

North Carolina: The biggest battleground state

The basics: Of the three states, North Carolina may be the most traditional battleground state. President Obama won it in 2008, then Mitt Romney won it in 2012, both by slim margins. Now, Clinton is pouring in millions of dollars.

And that plays perfectly into the hands of Democrat Deborah Ross, who is trying to unseat Sen. Richard Burr (R).

Republicans in Washington and North Carolina are frustrated that Burr isn't taking his challenge seriously — two higher-profile candidates passed on challenging him. He's up on TV, but they say he's not running the kind of breakneck campaign he needs to in a battleground state in a presidential year.

Meanwhile, Senate Democrats' campaign arm has poured in nearly $7 million to elevate Ross.

Where the race stands now: Burr has a 2.5-point lead, according to a RealClearPolitics average of recent polls, despite the fact that almost three-quarters of North Carolina voters don't know who his challenger is. That suggests this race is largely a function right now of politics at the presidential level — and there, Democrats have a slight edge.

We have the race leaning Republican, and recently bumped it from 10th most likely to flip to seventh.

What this race will probably come down to: How many black voters and millennials — both voting groups that favor Democrats — turn out. In 2010, Burr beat an underfunded challenger by eight percentage points, but he lost all the black-majority counties. And millennials are also the fastest-growing group in North Carolina.