Monday was the first day candidates could pull nomination papers for the May 21 special election to fill the state Senate seat recently vacated by Bakersfield Democrat Michael Rubio.

But just who will and who won't actually get those papers -- and then return them -- seems as up in the air as ever.

On Sunday, Hanford Republican Andy Vidak announced on his Facebook page that he would seek the seat. As of Monday afternoon, the post had 323 hits.

Vidak, who fought a pitched 2010 congressional battle before falling to incumbent Democrat Jim Costa, is well-liked in the west-side agriculture community.

But another Republican, Kerman Mayor Gary Yep, said Monday that he pulled nomination papers from the Fresno County Elections Office.

"I'm considering it closely," Yep said. "I'm not out."

A deciding factor for him, he said, was whether he would receive any party backing.

Like Republicans, Democrats are also scrambling to position themselves. Because of party registration, the seat is widely considered to be Democratic, but Republicans think they might have a chance to steal it away in a special election -- though holding it in a general election next year would be a challenge.

One Democrat who is out is Fresno County Supervisor Henry R. Perea, who follows his son, Assembly Member Henry T. Perea, in passing on a run. Either Perea would likely have cleared the field on the Democratic Party side, party observers said.

"It would have been an honor to serve the Valley at the state level; however, as county board chairman, my responsibility is to lead on issues important to our county," Perea said. "I will commit my full support to the candidate selected by Senate leadership."

With both Pereas out, it could come down to a three-way race among Leticia Perez, a former Rubio aide and newly elected Kern County supervisor; Shafter City Council Member Fran Florez -- whose son, Dean Florez, held the seat before Rubio; and Kings County Supervisor Richard Valle.

Perez and Valle each addressed the Fresno County Democratic Central Committee last week, and Florez and Perez are both headed to Sacramento this week to meet with Senate President Pro Tem Darrell Steinberg.

Former Assembly Member Nicole Parra of Bakersfield last week said she wouldn't seek the seat. Parra, who served in the Assembly as a Democrat but is now registered as "no party preference," was the top hope of Republicans looking to steal the seat. Parra likely would have caucused with the GOP.

Yep is scheduled to go to Sacramento this week as part of a local lobbying trip. He hopes to talk with Assembly Republican Leader Connie Conway of Tulare about the Senate seat when he is there.

Gov. Jerry Brown on Friday set May 21 as the election date to fill the seat of Rubio, who abruptly resigned almost three weeks ago. He was halfway through his first Senate term.

The window to pull papers began Monday. Anybody hoping to seek the seat must have their papers returned by March 29 -- which is just 17 days away.

The district that selects Rubio's replacement will be state Senate District 16 as it was between 2002 and 2012. Whoever wins will have to stand for re-election in the newly redrawn 14th Senate District. Both districts roughly run from Bakersfield north through Kings and part of Tulare counties, and include parts of Fresno County and a good chunk of the city of Fresno.