On a day expected to be dominated by GOP front-runner Donald Trump and the big prize of Michigan, it may be Texas Sen. Ted Cruz and the unlikely state of Idaho that steal the show.

Because of the way delegates are allotted in the states that are being contested Tuesday, Trump could win the large states of Michigan and Mississippi, but Cruz could still gain more delegates, allowing him to claim victory. The true decider will be the unassuming state of Idaho, where Cruz could bank enough delegates to win the day.

Recent polls give Trump fairly substantial leads in Mississippi and Michigan, the two largest states set to vote Tuesday. But both of those states’ GOP contests are fully proportional affairs, awarding delegates neatly along a percentage-of-the-vote basis.

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A new poll released Monday by Monmouth University also showed Cruz gaining on Trump in Michigan. Trump holds his lead with 36 percent of GOP voters surveyed and Cruz comes in second at 23 percent, a 10-point narrowing of Trump’s margin from the last public poll. Cruz scored victories in two of four contests Saturday, so the latest poll suggests he may be gaining momentum.

To Trump’s advantage, both Michigan and Mississippi are open primaries, contests where non-Republicans are allowed to vote. Trump dominates political independents who may vote in these GOP primary contests and have been doing so at record levels, drawn in by the front-runner’s non-traditional appeal.

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Let’s assume Cruz’s spurt of momentum and Trump’s strength in open primaries cancel each other out, freezing the results Tuesday to match the most recent polls from well-established outlets — an assumption that likely favors Trump.

[lz_table title=”Michigan Delegate Estimate with Current Polling” source=”Monmouth University”]Polling

Donald Trump,36%

Ted Cruz,23%

Kasich,21%

Rubio,13%

|Delegates

Donald Trump,25

Ted Cruz,18

Kasich,16

Rubio,0 (fails 15% threshold)

[/lz_table]

Using the Monday Monmouth poll for Michigan and a February 29 Magellan Strategies poll for Mississippi, Trump would pull 45 delegates out of those two states, Cruz 28, Kasich 16, and Rubio 9.

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Assuming Hawaii, which has no reliable recent public polls, is an equal wash between the candidates, then Trump leads Cruz 50 to 33 after those three contests.

The remaining contest in Idaho is a closed primary, a Republicans-only contest of the type that have favored Cruz to date. Of the six states won by Cruz in the GOP contest, all but his home state of Texas have been closed contests.

Idaho also fits the mold of a strong Cruz state due to its rural makeup. Five of six states won by Cruz — again, all but Texas — are in the bottom 15 states by population density in the country.

Idaho also has the important distinction of being a “winner take most” state, meaning if any candidate breaches 50 percent of the vote, that candidate takes all 32 delegates from Idaho.

In the closed contests Cruz won Saturday in Kansas and Maine, the Texas senator came within a few points of 50 percent in both. With the addition of some momentum from a strong performance Saturday and a campaign visit to Boise over the weekend, Cruz could well be in position to win the full 32-delegate prize from Idaho.

[lz_table title=”Current GOP Delegate Count vs. Projected Tuesday Outcome” source=”Associated Press and LifeZette”]Current GOP Delegate Count

Donald Trump,384

Ted Cruz,300

Rubio,151

Kasich,37

|After Tuesday

Donald Trump,434 (+50)

Ted Cruz,365 (+65)

Rubio,165 (+14)

Kasich,58 (+21)

[/lz_table]

If Cruz pulls off the Idaho sweep and results elsewhere come in as expected, the Texas senator will finish Tuesday with roughly 15 more delegates earned than Trump. That would leave the overall margin separating Cruz from Trump at just 69 delegates, a mere 19 percent of the delegates up for grabs on March 15.

Even if Cruz doesn’t breach the 50 percent threshold in Idaho, the delegate take both for him and Trump would still end close to a wash — meaning even Trump’s best-case scenario will underperform his hype headed into the Tuesday battle.

A delegate win on that day and the resulting momentum shift would be huge for Cruz, especially on the heels of his strong Saturday showing. There, he handily won contests in Kansas and Maine, tied Trump for delegates in Louisiana, and won the straw poll at the annual conservative grassroots confab called CPAC.

Trump has been expected to have a strong Tuesday by virtue of his lead in the larger states. A Cruz delegate win for the day would upset those expectations, and throttle speculation that Cruz is the true anti-Trump candidate but a fighter who could actually beat the current GOP front-runner.

Watch for results from Boise Tuesday night to determine who wins the day and marches towards the crucial March 15 primaries in Florida, Ohio, North Carolina and Illinois with momentum.