Before Los Angeles County Sheriff Lee Baca announced his surprise resignation this week, those campaigning to replace him mostly argued that the 15-year incumbent needed to go so leadership could be returned to the beleaguered department.

When former Undersheriff Paul Tanaka announced his candidacy atop a helicopter landing pad, he said county residents were "long overdue for a new direction from their sheriff." The prior day, former Cmdr. Bob Olmsted announced his bid, saying he was "running for sheriff to restore integrity."

Now the man who was their foil will be gone in three weeks, inexorably changing the campaign for both challengers, according to political analysts.

"They're going to have to talk about themselves and why they're the most qualified, and that makes it a totally different campaign all the way around," said Allan Hoffenblum, a former GOP strategist and publisher of the nonpartisan California Target Book, which handicaps legislative races. "There's no one to contrast with."

In one practical manner, Baca's decision helps them — despite the myriad scandals that unfolded under his watch, he would have been a formidable candidate. Baca had high name recognition in a county of 10 million people, a strong fundraising ability and deep ties to Los Angeles' diverse communities. Taking him on was never going to be easy.

But his departure is prompting many who once decided against running to reconsider. Already, Assistant Sheriff Todd Rogers has announced that he is joining the race; among those weighing a bid are Assistant Sheriff James Hellmold, Long Beach Police Chief Jim McDonnell and Los Angeles Police Department Deputy Chief Terry Hara.

Given the ongoing federal investigation of the sheriff's county jail management, which has resulted in the recent arrests of 18 current and former department members, voters may look elsewhere for a fresh start, as city leaders did when they appointed William J. Bratton from New York to take over the Los Angeles Police Department.

"I think it increases the likelihood that voters might start looking for someone outside of the department who is not tainted by any of the department's problems," Hoffenblum said. "It's going to be wide open."

Tanaka said Baca's retirement does not affect his campaign, which is focused on telling voters about his crime-reducing efforts during 33 years in law enforcement, as well as the fiscal responsibility he showed when managing the Sheriff's Department's budget and serving as Gardena's mayor.

He added that outsiders from other agencies have never dealt with a system as multifaceted as the county's Sheriff's Department, which is the largest in the world.

"The Sheriff's Department is a very complex operation, and I think experience is going to make a big difference when voters take a look" at the race, Tanaka said.

John Shallman, Olmsted's campaign consultant, said the former commander offers a mix of insider knowledge with an outsider's perspective. The consultant said Olmsted had a track record of ferreting out misconduct that occurred under Baca's watch, and going to the FBI when he believed that Baca and Tanaka ignored his warnings of problems in the jails.

"He's the guy who's been on the front lines of this battle, standing up every single day, talking about reforming this department," Shallman said. "Everyone else is going to be a Johnny-come-lately."

Shallman added that Olmsted ran because of his "political courage," while new candidates would be "political opportunists," driven by the conditions of the field rather than the department's needs.

"Now people are going to come out and say they're getting in for all the right reasons. I think voters are not looking for another politician to be in that office. I think quite the opposite," he said.

On Wednesday, Olmsted's campaign argued that Baca's retirement was the direct result of Olmsted going to the FBI with his concerns about misconduct in the jails, and the candidate called for a series of debates in the race.

"Voters deserve a thoughtful, in-depth, and spirited campaign where they'll have a real opportunity to learn about the candidates' backgrounds and their visions for the office of sheriff," Olmsted wrote in a letter to media outlets asking them to host debates.

One thing everyone can agree on is that the race will be unlike any sheriff's contest in more than half a century.

Traditionally, retiring sheriffs all but anointed their successors, with the exception of Baca's run in 1998. That year he was challenging his former mentor and boss, Sheriff Sherman Block, who appeared to be headed toward reelection until he died days before the voting.

"It's astonishing — we're looking at the first true, open and competitive race for sheriff in generations," said Raphael J. Sonenshein, executive director of the Edmund G. "Pat" Brown Institute of Public Affairs at Cal State Los Angeles. "It should certainly be an opportunity for voters to look at the widest range of candidates — it's like a big job interview."

seema.mehta@latimes.com