TALLAHASSEE (CBSMiami/NSF) — In another sign of “muddled” races, Congressmen Alan Grayson and Patrick Murphy are virtually tied in the Democratic primary for U.S. Senate, while Congressman David Jolly holds a slight lead among announced Republican candidates, according to a Mason-Dixon poll released Monday.

“There is no clear favorite in either primary race for Florida’s open U.S. Senate seat,” pollster Brad Coker said in an analysis accompanying the results. “In the current field of declared or highly likely candidates, no one currently appears to have enough strength to be labeled as the ‘front-runner.’ ”

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The race to replace Republican presidential candidate Marco Rubio likely will be one of the most-closely watched Senate contests in the country in 2016. But it has not attracted any candidates with big statewide names, leading to primaries that Coker described as “muddled to say the least.”

A Quinnipiac University poll released last month also showed that voters knew little about the candidates.

The Mason-Dixon poll, conducted last week, showed Grayson with the support of 33 percent of registered Democratic voters and Murphy with the support of 32 percent. The poll indicated 35 percent of Democrats were undecided in such a head-to-head match-up.

On the GOP side, the poll gave Jolly the support of 16 percent of registered Republicans. He was followed by Lt. Gov. Carlos Lopez-Cantera at 10 percent; Congressman Ron DeSantis at 9 percent; Congressman Jeff Miller at 8 percent; and Orlando businessman Todd Wilcox at 2 percent. A whopping 55 percent of GOP voters indicated they were undecided. Miller has not announced whether he will run for the seat.

The poll also asked voters about two potential wildcards in the Senate race: Democratic Congresswoman Gwen Graham and former state Attorney General Bill McCollum. Both have faced speculation that they will run for Senate, with the speculation about Graham largely fueled by an upcoming congressional redistricting process.

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Graham, the daughter of former Gov. and U.S. Sen. Bob Graham, trailed the other Democrats by double digits in a hypothetical contest, with Murphy at 26 percent, Grayson at 24 percent and Graham at 11 percent.

“It is apparent that most Florida Democrats statewide currently do not make the personal connection between her and her iconic father — former Governor and Senator Bob Graham,” Coker said in the analysis. “Over the course of a campaign that would change of course, and she certainly has great potential to become the heavy Democratic favorite over the next year. But she will have some work to do to get there.”

McCollum, meanwhile, would jump to the top of the Republican field. When his name was added to the poll, McCollum was at 22 percent, Jolly was at 11 percent, DeSantis was at 8 percent, Lopez-Cantera was at 7 percent, Miller was at 6 percent and Wilcox was at 1 percent.

In the analysis, however, Coker noted that McCollum has lost statewide races in the past, including the governor’s race in 2010 and two U.S. Senate bids.

“Given his history of losing early leads in several previous statewide races, that number (22 percent) would not be daunting enough to scare away any rivals,” Coker said.

Coker’s firm, Mason-Dixon Polling & Research Inc., conducted the poll from July 20 through Friday. It surveyed 500 registered Republican voters and 500 registered Democrats. The results said the margin of error is “no more than 4.5 percentage points.”

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The News Service of Florida’s Jim Saunders contributed to this report.