As Sen. Bill Nelson (D-Fla.) prepares to face voters in a state that has recently trended toward the GOP, there is little disagreement among political insiders that the freshman Senator could be vulnerable.

However, the picture is increasingly murky when it comes to assessing whom the Republicans might ultimately turn to in their effort to topple him.

Rep. Katherine Harris (R), who passed on a 2004 Senate run, has been the most oft-mentioned challenger. But GOP insiders are more and more convinced she will not run — a decision that many in the party privately cheer.

A spokesman for Harris maintained on Tuesday that she has not yet made up her mind on a Senate bid, choosing to focus on her legislative priorities instead of her political future.

“She thinks it’s very flattering that people have thrown her name in the hat,” said Garrison Courtney. He said the Sarasota Congresswoman will make up her mind about a run sometime in the next six months.

Polling indicates Harris, a former Florida secretary of state who played a starring role in the 2000 presidential recount, would run strong in a hypothetical Senate primary against current statewide office holders.

But the same polls have also shown she would be among the weakest general election challengers to Nelson, who is below the 50 percent mark in the same surveys.

Some Republicans also privately highlight the fact that Harris has underperformed in her staunchly Republican district — pointing to her 55 percent showing against an underfunded opponent in her past two House campaigns — as an additional illustration of why she would not be the party’s strongest nominee.

Despite her public declarations, there are some tangible indications that she may be leaning against a Senate run.

Chris Battle, Harris’ chief of staff, is leaving the office to return to Arkansas and work on the gubernatorial campaign of ex-Rep. Asa Hutchinson (R), his former boss. Courtney stressed that Battle’s decision was based on family considerations and nothing more.

Battle is the fourth person to serve as chief of staff since Harris was elected in 2002, although two of those longtime aides remain close to the Congresswoman.

National Republican Congressional Committee Chairman Tom Reynolds (N.Y.) headlined a district fundraiser for Harris in early February, an event some political operatives saw as the clearest indication yet that Harris will forgo a statewide bid.

If Harris doesn’t run (or even if she does), there is a wide range of alternative candidates for Republicans, although no clear frontrunner.

“There hasn’t been a lot of discussion out there about other names,” one Florida Republican conceded.

Many in the party remain hopeful that one of the three Republicans currently seeking to succeed Gov. Jeb Bush (R) in 2006 will eventually opt for the Senate race.

State Attorney General Charlie Crist, state Chief Financial Officer Tom Gallagher and Lt. Gov. Toni Jennings are all considered top-tier challengers to Nelson. There have been rumblings that Jennings may be ready to exit the governor’s race, but her interest in a Senate bid remains unclear.

Rep. Mark Foley (R), who ran briefly for Senate in 2004 and holds the door open to another run next year, expressed doubt that any of the three would be wooed into the Senate race.

“I don’t sense under any scenario with anybody trying to broker a deal, including George W. Bush, that he would get one of those three candidates to shift their focus to the seat in Washington,” Foley said.

Unlike the 2004 cycle, when GOP leaders, led by the White House, enticed then-Housing and Urban Development Secretary Mel Martinez into an open Senate race, the party has no go-to challenger now, Foley acknowledged. The nomination could easily be Jeb Bush’s for the asking, although the two-term governor has no interest in joining his brother in Washington.

Among the Republicans in the Congressional delegation, aside from Harris, Foley and Rep. Dave Weldon are most often mentioned.

Foley wouldn’t rule out a run next year, but acknowledged, “I’d have to really get reinvigorated for the challenge.”

Some Republicans also dream of coaxing freshman Rep. Connie Mack IV (R), the son and namesake of a former Senator, into the race. But a top aide to the Congressman laughed off the idea and said that his boss is seeking re-election in 2006.

“It’s a silly, ludicrous and absurd,” Jeff Cohen said. “Connie is focused on being a great Representative in the House.”

National Republican Senatorial Committee spokesman Brian Nick said Republicans have full confidence that a top challenger will emerge.

“There are several qualified candidates that have expressed interest in this race — further demonstrating the high level of confidence Republicans have in taking this seat and Senator Nelson’s extreme vulnerability,” Nick said.

Whoever Republicans eventually nominate, Foley said, can’t expect to cruise to victory even if the state has trended more Republican.

“Bill Nelson is not going to be an easy task,” Foley said. “Anybody that thinks an incumbent is easy has got to re-examine their head. He’s formidable. He works hard.”

Democrats say Nelson is well-prepared for a tough challenge and they have little doubt one will eventually materialize. At the end of 2004, Nelson had $2.1 million in reserves.

“Florida Republicans have good reason to be wary of taking on Bill Nelson,” said Democratic Senatorial Campaign Committee spokesman Phil Singer. “He’s done an excellent job for the people of Florida.”