Sen. Bill Nelson of Florida/Photo by Diego M. Radzinschi/ALM

A Washington-based super PAC backing Republican Senate candidates dispensed with what had been more subtle campaign hints aimed at U.S. Sen. Bill Nelson's age.

In a news release titled “Bill Nelson Tragically Forced to Admit His Memory Is Failing,” the Senate Leadership Fund on Wednesday pointed to Nelson saying a day earlier that he couldn't recall a 2010 letter he wrote to the U.S. Environmental Protection Agency about delaying the implementation of water-quality standards for Florida lakes, springs and other waterways.

“It's time for Bill Nelson's caretakers to keep better tabs on the Senator's whereabouts and public statements so that he is not embarrassed into admitting he's no longer dealing from a full deck,” Senate Leadership Fund spokesman Chris Pack said in the release.

The news release came amid an increasingly nasty race between Nelson, a Democrat, and Republican Gov. Rick Scott for Nelson's Senate seat.

The 8-year-old letter by Nelson, along with one written around the same time by Scott, also added to a fierce political blame game over water-quality problems across South Florida.

Nelson's campaign called the super PAC's news release “a desperate attempt to distract from Rick Scott's record of cuts and deregulation that helped create this toxic algae crisis.”

Nelson is 75, while Scott is 65.

Susan MacManus, a distinguished professor of government and international affairs at the University of South Florida, said such age-based attacks are becoming less effective.

“Look at younger voters' support for Bernie Sanders in 2016 and longer life expectancies among older voters,” MacManus said. “What polls are showing is more effective in an era of voter disgruntlement is candidates' longevity in office rather than their sheer age.”

Scott, a two-term governor, has worked to make Nelson's lengthy political career, which started in the Florida House in 1972, an issue in the contest.

Kevin Wagner, an assistant professor of political science at Florida Atlantic University, said “age attacks are nothing new,” noting how President Ronald Reagan spun such attacks by saying he would not “exploit for political purposes my opponent's youth and inexperience.”

“My suspicion is that politics has gotten so tribal, that these attacks are not going to move many Democrats,” Wagner said. “But Florida elections are close, and so just getting some more moderate voters to rethink their choices or even stay home because of age concerns might make the difference.”

Asked Tuesday, the day before the super PAC news release, about Scott's campaign making “subtle hints” about his age, Nelson responded with some indignation.

“Any time he wants to have a contest about push-ups or pull-ups, and we'll see who is not up to it,” Nelson told reporters before a dedication ceremony at a Tallahassee veterans' health care center.

When asked Tuesday about his 2010 letter to the EPA, Nelson said he would need to look up the issue.

“Not only do I not recall that, that simply could not be true,” Nelson said. “There must be a nuance there. So, I'll have to look at it and see.”

In the letter to the EPA, Nelson wrote: “Clean water is a goal we all share,” adding that he was sharing the concerns of residents, businesses, farmers and local governments about the “potential cost of compliance with these standards and the validity of the science.”

“That is why it is imperative that this regulation is finalized in a deliberative manner, utilizing sound science and considering the effects of implementation,” Nelson wrote in the letter. “Rushing to finalize the rule could result in further uncertainty and unnecessary economic hardship for municipal governments and Florida industry.”

His campaign noted that Nelson annually has hundreds of pieces of correspondence.

Nelson's letter was similar to a lobbying effort by Scott against the proposed changes after he was elected governor in November 2010. In a letter, Scott called the changes in water-quality standards “onerous” and requested a delay “so that we have time to fully analyze the rule” and its effect on Florida.

Jim Turner reports for the News Service of Florida.