It's officially fish-or-cut-bait time in the pitched battle for control of the Senate.

Politico reported Monday night that the Democratic Senatorial Campaign Committee canceled a week of reserved ad time in three states: Florida, Illinois and Wisconsin. That's good news for Democratic hopes in Illinois and Wisconsin, where polling has consistently shown Sens. Mark Kirk (R) and Ron Johnson (R) running behind their Democratic challengers, and less good news in Florida, where Sen. Marco Rubio (R) appears to be moving toward putting away the Sunshine State race.

While canceling ad time is not a foolproof sign that one side or the other is giving up, it's a pretty damn good one. It's the whole put-your-money-where-your-mouth-is thing. If you assume — as the DSCC seems to — that Florida, Illinois and Wisconsin are close to over, then Democrats stand at a two-seat gain. And with Democrats giving up in Ohio weeks ago, that state is off the table, too.

What those moves mean is this: There are now five states that will decide which side controls the Senate next year: Indiana, Nevada, New Hampshire, North Carolina and Pennsylvania.  Four of those five are currently in Republican hands; Nevada is an open seat created by the retirement of Senate Minority Leader Harry Reid (D).

If Democrats hold Nevada — more on that below — they need to win two of the four remaining seats to control the Senate if Hillary Clinton is elected president. They need to win three of the four if Donald Trump is elected.

At the moment, Democrats' best bet for a pickup out of that quartet of states is Indiana, where former senator Evan Bayh (D) continues to lead Rep. Todd Young (R) — although both sides acknowledge that the race is tightening amid a GOP onslaught on the amount of time Bayh has spent in Washington since leaving the Senate six years ago.

Pennsylvania moved toward Democrats — and against Sen. Pat Toomey (R) — in the aftermath of the two national political conventions, and it hasn't swung back since. Toomey is running a serious and centrist campaign but is struggling to distance himself from the Republican brand nationally. His opponent, Katie McGinty, has been unspectacular but benefits hugely from being a Democrat in a Democratic-leaning state in a presidential-turnout year.

North Carolina's Richard Burr (R) has the opposite problem of Toomey: He's in a good(ish) state to be a Republican but has run a very poor campaign. Burr is not helped by the fact that Trump and Gov. Pat McCrory (R) have done him no favors at the top of the ticket. Republicans have just begun pummeling former state representative Deborah Ross with ads focused on her record as an ACLU lawyer, commercials they believe will be a silver bullet in the race.

New Hampshire is extremely close — as it has been since the day Gov. Maggie Hassan (D) decided to challenge Sen. Kelly Ayotte (R). Ayotte continues to struggle with what to say about Trump, offering tortured responses about the difference between voting for him and endorsing him. (BREAKING: There's no difference!) On Monday night, Ayotte made her Trump problem worse by saying, in a debate, that he was "absolutely" a role model for kids. Within hours, Ayotte was backtracking.

The big "if" buried in all of the analysis is Nevada. Remember I said that if Democrats hold Nevada, they need to win only two or three of the four remaining Republican target seats to retake the majority. But, right now, Democrats aren't winning Nevada.

Rep. Joe Heck (R) leads former state attorney general Catherine Cortez Masto by 3.5 points in the Real Clear Politics polling average. And Heck has led in nine of the 11 polls conducted in the race since May. (One survey showed the race tied, the other had Cortez Masto up by two points.

A Heck win makes a Democratic Senate a much longer shot; the party would need to win at least three of the four GOP-held seats even if Clinton were elected president and sweep all four in the event of a Trump victory.

That's not impossible. If history is any guide, the toss-up races tend to all move in one direction in the final weeks of the campaign. If they all move toward Democrats, the party will win the majority — maybe with a few seats to spare. If Republicans get a slight tailwind, however, they could — against all odds — hold on to their majority for two more years.

Either way, it's all down to five states now. That's where to look in the final five weeks of this campaign.