WASHINGTON—Georgia Democrat Stacey Abrams isn't the only Democratic star of 2018 taking a pass Tuesday on a Senate bid. 

Iowa Democratic Rep. Cindy Axne will run for re-election instead of challenging Republican Sen. Joni Ernst for her Senate seat, making her the latest Democrat to decide against running in a pivotal Senate race. 

Axne, who flipped a GOP-held House district for Democarts in the Hawkeye State in 2018 when she defeated Republican Rep. David Young, had been seen as a top prospect for Democrats looking to dethrone Ernst. 

But an Axne spokesperson confirmed with NBC News on Tuesday that the freshman congresswoman will run for reelection to her House seat instead of running. 

That leaves Democrats still looking for a candidate to run against Ernst, who had a 57 percent approval rating in a recent Des Moines Register poll. 

Nathan Brand, the National Republican Senatorial Campaign spokesman, needled Senate Democrats over the decision, arguing that possible Democratic candidates "know Senator Joni Ernst's record of delivering results for Iowans puts her in a strong position for re-election."

Democrats need to flip three Senate seats in 2020 and win the White House (or flip four seats if President Trump wins reelection) to regain control of the Senate. 

The party's best chances of flipping GOP-held seats appear to be in Colorado and Arizona, but Alabama Democratic Sen. Doug Jones will have a tough reelection fight in Alabama.

So if Democrats can win in Colorado and Arizona, while losing in Alabama, that means they'll have to win two of the races in Maine, Georgia, North Carolina, Iowa, Kentucky or Texas. 

But even though it's early in the cycle, Democrats are still looking for premiere candidates in a handful of those races. 

Read more about how the battle for the Senate is shaping up in today's edition of the Meet the Press: First Read newsletter. 

UPDATE: This article was updated to include a statement from the NRSC. 

--Ben Kamisar contributed