First Read: Is Trump losing momentum? Tuesday will tell

First Read is a morning briefing from Meet the Press and the NBC Political Unit on the day’s most important political stories and why they matter.

Is Trump Truly Losing Momentum? We’ll Find Out Tonight

Tonight’s primaries in Michigan and Mississippi — as well as the contests in Idaho (primary) and Hawaii (caucus) — are important for Donald Trump to regain his momentum heading into next week’s winner-take-all primaries and increase his narrow delegate lead over Ted Cruz.

Is Trump losing ground? Or were last weekend’s results due more to the fact that they were closed contests (not open to non-Republicans)? We’ll find out tonight. Both Michigan and Mississippi are open primaries, and Trump SHOULD win them by double digits; Trump is way ahead in the Michigan polls.

Indeed, a state like Michigan (remember the Reagan Democrats of Macomb County?) should be the heart and soul of the Trump movement. If he doesn’t win — and win convincingly — you have to ask yourself if something is going on after Thursday’s debate and Mitt Romney speech.

Rubio’s Staring at the Possibility of Fourth-Place Finishes in Michigan and Mississippi

Meanwhile, tonight is equally important for Marco Rubio, who is staring at the distinct possibility of two fourth-place finishes in Michigan and Mississippi. Yesterday, CNN reported that some Rubio advisers are contemplating getting out of GOP race before the Florida contest — which the Rubio campaign vigorously denies. Here’s why Rubio getting out now would be crazy: Due to the early voting in state, Rubio exiting the race would automatically hand Florida (and maybe the GOP nomination) to Trump. And there’s no way Rubio wants to get blamed for giving Trump an easy win.

Bernie’s Last Stand

Over the last few days, Bernie Sanders has been acting like there’s no tomorrow after tonight’s Michigan primary — he came out swinging in Sunday’s debate, he’s launched some of his toughest attacks on Hillary Clinton (on trade), and he’s out-advertising her in the state. And there’s a good reason for that: If he doesn’t win tonight, there won’t be a tomorrow when it comes to a competitive Democratic horserace.

Don’t get us wrong, Sanders has plenty of money (he raised $40 million-plus last month) to keep his campaign alive through June; he’ll continue to win contests, especially caucuses; and he’s run a stronger race against Clinton than anyone could have imagined six months ago. But a loss in Michigan would:

• Prove he can’t win in big, diverse states;
• Deny him the momentum he needs going into next week’s contests in Florida, Illinois, Missouri, North Carolina, and Ohio;
• And pretty much end the chances of Democratic superdelegates changing their minds.

So a lot is riding on a Michigan win for Sanders. And we haven’t even discussed the delegate math, where Clinton holds a 199-delegate lead over Sanders in pledged delegates, 669-470, and a 600-delegate lead when you add superdelegates, 1100-492. Clinton knows what’s riding on Michigan, too. “The sooner I could become your nominee, the more I could begin to turn attention to the Republicans,” she told Michigan voters last night, per NBC’s Monica Alba.

Tonight’s Four Contests

Tonight features four contests — primaries in Michigan (D & R), Mississippi (D & R) and Idaho (R), and caucuses in Hawaii (R). Final polls close in Mississippi at 8:00 pm ET, in Michigan at 9:00 pm ET (four counties are in Central Time Zone), and in Idaho at 11:00 pm ET. And doors close for the Hawaii caucuses at 1:00 am ET.

Trump: “Until This Phone Call, I didn’t know [Supporters Raising Their Hands] Was a Problem”

Trump called into “Today” this morning, and was asked about the criticism of supporters raising their hands to pledge their votes at rallies. “Sometimes, we’ll do it for fun,” Trump responded. “Honestly, until this phone call, I didn’t know it was a problem.” So we’ll take Trump at his word: We assume this kind of activity will no longer occur, right?

This week’s NBC|SurveyMonkey Online Tracking Polls

In the Democratic race, Clinton leads Sanders by 17 points, 55%-38% — up from 51%-41% last week. And in the Republican race, it’s Trump 39% (-1), Cruz 20% (+2), Rubio 18% (-3), and Kasich 9% (+2).

Michael Bloomberg All But Endorses Hillary Clinton”When Michael Bloomberg announced that he would not run for president, he did not quite endorse Hillary Clinton. But you could read that endorsement between the lines,” Business Insider’s Josh Barro writes. And we agree. Just look at what Bloomberg said: “As the race stands now, with Republicans in charge of both Houses, there is a good chance that my candidacy could lead to the election of Donald Trump or Senator Ted Cruz. That is not a risk I can take in good conscience.”

On the Trail

Hillary Clinton holds a rally in Cleveland at 7:00 pm ET, while Bill Clinton stumps in Illinois and Missouri… Donald Trump holds a press conference in Jupiter, FL at 9:00 pm ET… Bernie Sanders holds a rally in Miami, FL… Marco Rubio stumps in Florida… Ted Cruz is in North Carolina… And John Kasich stumps in Michigan and Ohio.

Countdown to FL, IL, MO, NC, OH contests: 7 days

This article first appeared on NBCNews.com.