Senate Democrats have been scrambling to prevent two of their members from taking a post in the Trump administration, trying to prevent any defection that could bolster Republicans’ control of the chamber.

They recently launched a “full court press” to retain Sens. Joe Manchin, of West Virginia, and Heidi Heitkamp, of North Dakota, after each met with Republican President-elect Donald Trump, one senior Senate Democrat told Fox News.

Manchin now appears less likely to bolt -- after saying he wants to remain in the Senate and being passed over for Energy secretary -- which puts the focus squarely on Heitkamp.

The first-term lawmaker, who faces reelection in 2018 in a conservative state, still appears in the running for the Agriculture secretary post.

A Trump transition team source told Fox News the president-elect “really wants her” for the job.

Either departure would pose short- and long-term challenges for Senate Democrats.

If Heitkamp left, her seat could remain empty for months, meaning Democrats would have one less vote to stop any of Trump’s first-100-day initiatives, which could including getting a Supreme Court nominee confirmed in the Senate or passing a tax overhaul.

The North Dakota legislature last year changed its laws so that a Senate seat remains vacant, without a place-holder senator, until it is filled in a special-election vote held within 95 days of a resignation.

In the longer-term, Senate Republicans would have a solid chance of winning Heitkamp’s seat in a special election and adding to their 52-48 member majority.

In West Virginia, the governor would under the law appoint a temporary replacement and hold a special election within 48 to 120 days to fill the seat for the remainder of the term which ends in 2017.

West Virginia’s Democratic governor likely would appoint a Democrat to fill the seat in the interim.

As a Democrat in an increasingly conservative state, Manchin initially had appeared at risk of leaving.

And his words and actions in recent weeks -- criticizing Senate Democratic leader Harry Reid and risking a government shutdown over coal miner benefits -- suggested a willingness to depart the Senate, or at least prepare for a tough reelection fight in 2018 in a state that went for Trump over Democrat Hillary Clinton 68-26 percent.

Manchin last month chastised Reid for calling Trump after his White House win a “sexual predator,” saying Reid’s remarks were an “absolute embarrassment” and “needlessly … tearing this country apart.”

Reid recently told CNN that Manchin’s comments were “his way to get out the door.”

Democrats, in an apparent effort to solidify their caucus, recently made Manchin part of their leadership team. And Trump’s official decision Wednesday to pick former Texas Republican Gov. Rick Perry for Energy secretary, for which Machin was being considered, settled the speculation for now.

“I was humbled to be considered for the Secretary of Energy position,” Manchin said in a statement. “I have dedicated my life in public service to doing what is best for the people of West Virginia. Right now, I believe that I can best serve my state of West Virginia in the United States Senate.”

Heitkamp and Manchin are among 10 Democrats in the chamber seeking reelection in 2018.

Trump has only three remaining Cabinet posts to fill -- Agriculture, Interior and Veterans Affairs.

FoxNews.com's Joseph Weber and Fox News' Bret Baier and John Roberts contributed to this report.