The stakes couldn’t be much higher in the race to replace ex-state Sen. Dean Skelos, the Long Island power broker convicted of corruption.

Losing the seat, based in southwest Nassau County, could bode ill for the Republicans’ chances to hold on to the Senate, the one area of state government they control, though with a thin majority.

It could be key for the Democrats’ long-sought goal of eventually flipping control of the chamber and test their attempts to make inroads in Senate races on Long Island this year. It also could impact the 2016 legislative agenda.

As 2016 opens, the statewide political focus will be on a vacancy in Nassau County.

“This is a big race, especially when you have that kind of razor-thin majority in the Senate and since Nassau County has become a lot more competitive than the days when the Republicans could run a post and win,” said Michael Dawidziak, a Bohemia-based political consultant who works mostly with Republicans.

Skelos was expelled automatically from the Senate when he was convicted in U.S. District Court on Dec. 11 along with his son, Adam, on eight counts of extortion, bribery and conspiracy. They are expected to appeal.

The departure of the Rockville Centre Republican leaves the Senate with 31 Republicans and 31 Democrats — although the GOP is still in control because state Sen. Simcha Felder (D-Brooklyn) sits with the Republican conference. Also, five breakaway Democrats known as the Independent Democratic Conference joined a governing coalition with Republicans.

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It will be up to Gov. Andrew M. Cuomo to set a date for a special election to replace Skelos. Though he hasn’t weighed in on the Skelos race, Cuomo has said he’d likely set a special election to replace former Assembly Speaker Sheldon Silver — convicted of corruption 12 days before Skelos — on April 19, leading the parties to start planning for that date. Technically, a special election must occur within 90 days of a governor calling it, so the date might not become official until later this month.

The parties could spend upward of $4 million on the race, some said.

The broad themes of the campaign are already clear: corruption, change and “regional balance.”

Democrats will try to tie any GOP candidate to Skelos, and will note that Senate Republicans blocked proposals to overhaul campaign-finance laws and ban lawmakers’ outside income.

“Let’s remember that this vacancy exists because of corruption, and whichever candidate the Republicans put forward will have been taught at Dean Skelos’ knee,” said state Sen. Michael Gianaris (D-Queens), head of the Senate Democrats’ campaign committee.

Republicans say a Democratic-led Senate will make state government too focused on New York City. They point to 2009-10, when Democrats briefly controlled the chamber and imposed an unpopular payroll tax amid a recession. The tax since has been largely repealed.

“Voters understand who has stood up for Long Island and that’s been Senate Republicans,” said Senate GOP spokesman Scott Reif.

Even a Suffolk County Democrat said that argument will play well with some Long Islanders.

“That’s going to be a big hurdle for any Democrat running,” said Patrick Halpin, a former state assemblyman and Suffolk County executive. “They’re going to have to make it clear that under no circumstances would they support something like the [payroll] tax, and they will work for the region, not the party.”

But Republicans also will have to get out of Skelos’ shadow, Halpin said, adding that “as far as voters are concerned, the Skelos seat is ground zero for political corruption in Albany.” He noted that, in the recent contest for Nassau County district attorney, Democrats sought to tie Republican Kate Murray to Skelos. Democrat Madeline Singas won the race.

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Figuring corruption will be a key talking point, some Democrats want Assemb. Todd Kaminsky (D-Long Beach), a former federal prosecutor whose Assembly district covers much of Skelos’ Senate district, to run.

Other potential Democratic candidates include former Nassau County clerk candidate Laura Gillen and Nassau Legis. Carrié Solages (D-Elmont).

Assemb. Brian Curran (R-Lynbrook), Hempstead Town Councilman Bruce Blakeman and Nassau Legis. Howard Kopel (R-Lawrence) and Denise Ford (R-Long Beach) are among the possible Republican contenders.

Timing of the special election likely will also play a role. April 19 is the date of New York’s presidential primary. Democrats fear their side might see a low turnout because Hillary Clinton has a chance to seal the nomination by then. That could mean a comparatively better turnout for Republicans because the GOP will still have a number of contenders.

Further, local Republicans historically have fared better in special elections, which can turn on get-out-the-vote efforts and absentee ballots.

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“This race is important on several levels,” said Lawrence Levy, a Hofstra University political analyst, citing the balance of power in the Senate, the 2016 legislative session and fall elections.

“It’s a test of strength between the Nassau Republican and Democratic parties in terms of their organization and appeal, and ultimately more than a hint about which will be in a better position to control the fate of one of the country’s most important suburbs,” Levy said.