The Florida race for U.S. Senate seat appears to be turning into a voters’ choice for the most acceptable candidate when deciding between two unpopular choices and perhaps a missed opportunity for Republicans.

In their quest to regain control of the Senate, Republicans took early aim at two-term Democrat Sen. Bill Nelson, portraying him as a Washington insider who was past his prime.

However, GOP Rep. Connie Mack IV has failed to capitalize on those advantages and has fallen behind in recent polls.

Mack trail Nelson by 7 percentage points, according to a Sept. 4 poll by Democrat-leaning Public Policy Polling. The poll also gave Nelson a favorability rating of 35 percent compared to 27 percent for Mack. The 69-year-old Nelson was leading by 2 percentage points, according to a July poll by the firm.

In addition, a poll released this week by Mason-Dixon Polling and Research shows Nelson leading Mack 48 percent to 40 percent, a three-point gain compared to the nonpartisan firm’s July poll.

The Mack campaign says the polls show Nelson’s campaign has stalled and that he cannot reach the all-important 50 percent, despite “a month of spending millions of dollars running perhaps the most obnoxiously negative personal smear campaigns” in the history of Florida politics.

“The people of Florida … want and deserve a senator who will stand with them and fight for them – not a 40-year,  career politician who tells them one thing and then votes like a lock-step liberal with Barack Obama,” Mack campaign manager Jeff Cohen said Friday.

Perhaps the most positive number out of the recent polls was the percentage of undecided voters in the Mason-Dixon telephone survey of 800 registered voters – an unusually high 11 percent.

While Republicans are trying to ride the anti-incumbent wave that helped them in 2010 win control of the House, Democrats have publicized Mack’s incidents of road rage and fights to portray him as too volatile for public office.

Democrats hold 23 of the 33 Senate seats up for grabs in November. They also have a 51-47 majority and votes from two independent senators, which mean Republicans would need a net gain of at least four seats on Election Day.

The Nelson campaign says the 45-year-old Mack -- the son of a senator, great-grandson of a baseball legend and husband of the widow of the late Sonny Bono –trails despite huge financial support from outside money.

 “What’s interesting is this comes after there have been $9.2 million in false and negative TV ads against Nelson from outside groups and super PACs tied to the Koch brothers, Karl Rove and undisclosed corporate dollars behind the U.S. Chamber of Commerce’s political attack arm,” said the campaign, according to The Orlando Sentinel.