Florida Gov. Rick Scott (R) leads Sen. Bill Nelson Clarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (D) by 4 percentage points in a new poll out Wednesday that underscores the tight nature of what's expected to become the most expensive Senate race in history.

Scott, who announced his Senate bid last month, is leading 44 percent to Nelson's 40 percent in Florida Atlantic University's survey. That's a shift from the university's February poll, which had Nelson up 2 points.

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But among voters who consider themselves "very likely" to vote in November, both candidates are tied at 45 percent each.

The poll is a mixed bag for Republicans, with Trump reaching a 43 percent approval rating — his highest in the university's polling since his inauguration. But the majority of voters said that the GOP's tax cuts have had no impact on their financial situation, and 49 percent said they'd rather have former President Obama return to office than continue with Trump.

Republicans are optimistically eyeing Nelson's seat, boosted by Trump's victory in the state in 2016 as well as by improving approval numbers for Scott and the governor's deep pockets.

But Democrats believe Scott's ties to Trump and controversial pieces of his tenure in office will hold him back, and are hopeful that strong Democratic turnout helps boost Nelson.

Wednesday's survey comes exactly one month after Scott first announced his bid.