A look at the battle for the U.S. Senate

Sometimes, it feels as if Senate Republicans are playing Whac-A-Mole in their attempt to keep control of the Senate in November.

They're now favored to hold the Senate. That's thanks in large part to candidates in Ohio and Florida pulling ahead of their Democratic challengers, sparing their party from having to spend 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 becomes vice president and is the Senate's tiebreaker.

• Indiana's open Senate seat — Republican Sen. Dan Coats is retiring — wasn't on most people's radar until recently. The state had a 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 Young.

Then Coats' rival, former senator and Gov. Evan Bayh, changed all that. He jumped into the race in July, apparently persuaded by arguments that Trump's unpopularity, along with Bayh's $10 million leftover war chest, would be a winning combination for him.

The race is now a tossup, and third most likely Senate race in the U.S. to flip parties.

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 take root. The National Rifle Association has launched more than $600,000 in ads criticizing him.

• Missouri: This race always had the potential to be competitive in a wave year for Democrats. But even absent any indication of a tidal wave of support for Democratic candidates across the nation, it's suddenly looking competitive.

Republican Sen. Roy Blunt 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 match his blind performance.

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.

Where the race stands now: The average of recent polls tracked by RealClearPolitics showed Blunt up by 3.4 points. The race is now leaning Republican and is the 10th most likely Senate race 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: 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.

That plays perfectly into the hands of Democrat Deborah Ross, who is trying to unseat Republican Sen. Richard Burr.

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 airing TV ads, but they say he's not running the kind of breakneck campaign he needs to in a battleground state in a presidential year.

That suggests that this race is largely a function right now of politics at the presidential level — and there, Democrats seem to have a slight edge.

The race is 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 — groups that favor Democrats — turn out. In 2010, Burr beat an underfunded challenger by 8 percentage points, but he lost every black-majority county. Millennials are the state's fastest-growing group.