Tallahassee Democratic Mayor Andrew Gillum is basking in the national spotlight as polls show him with a slight lead over Republican Ron DeSantis in Florida’s closely watched gubernatorial race. But an ongoing FBI probe into possible corruption in Tallahassee continues to cause headaches for his campaign just a week before the midterm elections – while fueling a fiery war of words between him and President Trump.

Gillum has long denied wrongdoing and said the FBI has told him he is not a focus of the investigation. But Republicans are doing everything they can to draw attention to Gillum’s link to the probe.

On Monday, President Trump referenced the probe on Twitter and called Gillum a “thief.”

Gillum responded that Trump “is howling because he's weak.”

Then it got much nastier. Trump doubled down in an interview with Fox News’ Laura Ingraham, calling Gillum a “stone-cold thief” and claiming he shouldn’t be allowed to run.

“He’s a total disaster,” Trump said.

Gillum tweeted in response that Trump was lying about him, “But as my grandmother told me — never wrestle with a pig. You both get dirty, but the pig likes it. So ignore him and vote, Florida!”

The fiery dispute served to further elevate Gillum's national profile, while also drawing attention to an issue that's been following his campaign for months back home.

According to local news outlets – which have extensively covered the case – the FBI has been investigating potential corruption related to land deals in the city. Last year, the FBI issued subpoenas for documents from the city of Tallahassee related to developers.

Gillum in 2016 also interacted with an undercover FBI agent who was posing as a businessman interested in investing in Tallahassee, according to those reports. He was introduced to that agent by lobbyist Adam Corey, a longtime friend who has since been subpoenaed as part the probe.

According to the Tampa Bay Times, Gillum scheduled a meeting with the undercover FBI agent while on a Costa Rica vacation with Corey in 2016.

More revelations have trickled out in recent days: Last week, the Tallahassee Democrat reported that the undercover agent was sent an invoice for $4,386 after agreeing to pay for food and drinks at a fundraiser for Gillum’s political action committee in 2016.

The Tallahassee Democrat referred to the revelation as the “first piece of evidence linking an ongoing FBI probe to Gillum's broader campaign for statewide office.”

Separate from the FBI investigation, Gillum’s past actions are also being scrutinized by the state Commission on Ethics. That ethics probe recently revealed that Gillum accepted tickets to “Hamilton” from the undercover FBI agent in 2016.

Gillum claimed last week he thought the ticket came from his younger brother, acknowledging “I should have asked more questions.”

In August, Gillum scored an upset victory in Florida’s gubernatorial primary over more establishment Democrats. After his primary win, he was showered with praise from big Democratic socialists like Bernie Sanders and Alexandria Ocasio-Cortez.

Since his victory, Gillum has made frequent nationally televised appearances, including on Fox News, CNN and MSNBC.

Gillum and DeSantis are running to replace outgoing GOP Gov. Rick Scott, who is term-limited. Scott is running against incumbent Democratic Sen. Bill Nelson in one of the most closely watched Senate races.

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In the governor’s race, most polls show Gillum with a slight advantage over DeSantis: the Real Clear Politics polling average has Gillum up 3.2 points over the Republican. The Fox News Power Rankings lists Florida as one of eight “tossup” races.

DeSantis and Gillum squared off last week for their final debate – in which Gillum called DeSantis a liar, said he should be disqualified and questioned his taxpayer-funded trips while in Congress.

“Release the receipts, it’s that simple,” Gillum said, accusing DeSantis of using the “Trump handbook” to run against him.

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Meanwhile, Gillum has also faced criticism over recent comments about law enforcement during an appearance on a liberal podcast. Speaking on “Pod Save America,” Gillum said “at the time that a law enforcement official has to go to a weapon, to a gun, to a baton, to a Taser," then they've already gone "too far by their very presence."

Appearing on “Fox & Friends” on Saturday, Brevard County Sheriff Wayne Ivey called Gillum’s comments “disgusting.”

“Andrew Gillum has no idea what it takes to serve as a law enforcement officer,” Ivey said.