Andrew Gillum's gubernatorial campaign may come down to one question: How much does Bernie Sanders' support matter in a Democratic primary?

The Independent Senator from Vermont is coming to Tampa on Friday to campaign with Gillum, the Tallahassee mayor who's taken up Sanders' progressive banner in the Florida governor's race. But with less than two weeks to go until the Aug. 28 Democratic primary — and hundreds of thousands of Democratic ballots already filled out — Sanders' visit comes at a make-or-break time for Gillum's gubernatorial hopes.

Gillum, who secured Sanders' endorsement earlier this month, has polled well behind former Congresswoman Gwen Graham and former Miami Beach Mayor Philip Levine in recent surveys. But around one in five primary voters remain undecided, and Gillum supporters hope Sanders can help sway those voters.

If it's not too late.

"When you're running for office, you want to peak on election day. You don't want to peak too early," Hillsborough County Commissioner Les Miller, who's endorsed Gillum, said Wednesday. "The other candidates have already peaked."

Sanders' backing of Gillum is just one in a recent slate of endorsements from national progressives and progressive groups for the self-described "most viably progressive candidate for Governor in Florida's history." Gillum also has the approval of the Working Families Party, the Progressive Change Campaign Committee, Our Revolution and Indivisible.

Related: Read more about Andrew Gillum's endorsements here.

But it's unclear whether all of those endorsements portend a primary win for Gillum. A recent analysis by the politics and polling website fivethirtyeight.com showed that Sanders and those groups have mixed records when it comes to picking winning candidates. Of the nine Democrats Sanders has backed in primaries, just five have won. (By comparison, Democratic U.S. Sen. Elizabeth Warren has endorsed five winners out of five.)

For his part, Sanders has made the argument that even if his preferred candidate loses, it's possible for that candidate to advance the "progressive cause."

Making a political revolution is not easy, and we should be enormously proud of the progress we are making across the country. @AbdulElSayed & @BrentWelder ran in what we knew from the start would be difficult races, and advanced the progressive cause in very significant ways. — Bernie Sanders (@BernieSanders) August 9, 2018

Gillum's campaign argues the Tallahassee mayor has done just that in the Florida primary.

"When we talk about the progressive issues that matter to people — Medicare for all, marijuana legalization — those are the issues that this campaign has led on," Gillum's communications director Geoff Burgan said.

Whether Gillum wins or not, Sanders' visit is sure to fire up the local left flank of the Democratic Party — the crowd that supports those lefty policies.

"I think (Sanders) is the face of the progressive arm of the Democratic party nationally," Ione Townsend, the chair of the Hillsborough County Democratic Party, said. "His coming to Tampa is going to thrill people who share his values."