Three decades after Democratic Gov. Bob Graham became the last challenger to defeat an incumbent senator in Florida, Republican Rick Scott’s attempt to return the favor is proving more difficult than expected.

Scott is leaving the governor’s mansion after two terms in office – possibly the best perch from which to unseat a sitting senator, whose job responsibilities and accomplishments are by definition far vaguer than those of the state’s chief executive.

And Democrat Bill Nelson seemed a relatively easy target. The former state insurance commissioner and, before that, congressman had never had a high-profile role in Washington. After three full terms as senator, his biggest claim to fame remains his ride to orbit as a passenger aboard a NASA space shuttle in 1986 when he was still in the House.

Despite this, though, Scott appears to be at best tied with Nelson in the polls with five weeks until Election Day – despite an enormous financial advantage that let him start running television ads months before Nelson and his allies could start airing them.

“Times have definitely changed from when he first ran for governor,” said Aubrey Jewett, a political science professor at the University of Central Florida in Orlando.

Scott rode the Tea Party wave of anger against then President Barack Obama in 2010, and then again in 2014, to win razor-thin victories notwithstanding his own unpopularity.

This year, even with improved approval ratings, Scott’s biggest problem is one he shares with most Republicans around the country: his political ally in the Oval Office, President Donald Trump, whose words and behavior have energized Democrats and many independents to vote against Republicans.

On top of that are three Florida-specific issues that appear to be hurting Scott now despite having helped him in previous years.

Eight years ago, Scott made opposing Obama’s Affordable Care Act a centerpiece of his campaign and then, as governor, refused to take part in the law’s Medicaid expansion in Florida. In a debate with Nelson Tuesday, Scott reflected the position of many Republicans around the nation who are now shifting positions on the law. “We have got to make sure we take care of people with pre-existing conditions,” he said, even though Florida is among the states suing to have the ACA’s pre-existing condition protection struck down.

As governor, Scott also signed every pro-gun rights bill that came to his desk from the National Rifle Association-friendly state legislature, including one to punish doctors who asked patients about their access to guns. That pattern shifted only this year after 14 students and three staff were gunned down by a former student with an assault-style rifle at Marjory Stoneman Douglas High School in South Florida. Scott, already running for the Senate, pushed for and signed legislation that includes some modest limits on gun owners. “Within three weeks of the Parkland shooting, we passed a comprehensive bill,” Scott said in Tuesday’s debate – to which Nelson countered: “My opponent has an A-plus rating from the NRA.”

But while the fight over Obamacare has dragged through the years and the Parkland shooting took place eight months ago, Scott’s most troublesome issue could be the twin environmental disasters of red tide and blue-green algae, which continue to torment residents and visitors in – ironically – some of the most heavily Republican counties in the state.

The red tide is responsible for killing millions of fish, sea turtles and dolphins, while the algae are clogging waterways from Lake Okeechobee to both the Gulf of Mexico and the Atlantic Ocean. Some researchers believe the algae blooms – caused by excessive fertilizer, cow manure and leaky septic tank waste running into the lake – are exacerbating the bacterial red tide.

“Most political issues are abstract,” said Jewett. “The issue of red tide and the toxic blue-green algae is quite the opposite. It is literally in your face and in your eyes and in your wallet.”

Scott’s problem is that he slashed budgets and positions at the Department of Environmental Protection and the state’s water management districts while dramatically reducing the emphasis on enforcement of pollution standards. As a result, nutrient levels that had started to decrease under the two previous Republican governors began increasing again under Scott’s watch.

“His record is very clear on the environment,” Nelson said at the debate.

While Scott has tried to blame the water quality problem on Nelson for failing to win more federal money to solve it, that argument may not wash with voters, said University of Florida political scientist Daniel Smith.

“It does not help Rick Scott. He’s had eight years to deal with this issue,” he said.

Smith added that while traditionally Republican voters in Fort Myers on the southwest coast or Stuart across the state might not flip and vote for Nelson, they may just skip voting in the Senate race. “Or they might not vote at all,” he said.

If they do not, and Nelson wins a close race and a fourth six-year term despite Scott’s many advantages, it would be his third stroke of good fortune come re-election time.

In 2006, Nelson ran in a traditionally Republican-leaning midterm year but which happened to be a Democratic wave election because of anger toward President George W. Bush and the Iraq War. Nelson also drew as his opponent Katherine Harris, the former secretary of state whom Democrats despised because of her role in securing a Florida victory for Bush in the disputed 2000 election.

Six years later, Republicans nominated Fort Lauderdale-area congressman Connie Mack IV, whose history of minor scandals – from getting into bar fights to road rage incidents ― made him relatively easy to beat.

“For Bill Nelson, the re-election winds have always proved favorable,” said Adam Goodman, a longtime Republican consultant who once worked for Harris. “Ironic that this year a red tide could help usher in a blue wave and Bill Nelson.”