CAPE GIRARDEAU COUNTY, MO (KFVS) - Arizona Senator Jeff Flake announces he will not be running for re-election.
Flake has been a vocal critic of President Donald Trump.
He now becomes the second Republican Senator after Tennessee's Bob Corker to give up his seat.
This possible shake-up could cost the Republicans both seats in the Senate.
But, a professor at Southeast Missouri State University says it's more likely that if they lose a seat, it would be one or the other.
Professor Jason Sides said that he believes that the seat more up for grabs is Senator Jeff Flake's in Arizona.
With increasing competition in the past few elections in Arizona, not having the incumbent could hurt the GOP in their election.
He also thinks that while President Trump was a factor in him stepping down there may have been other reasons.
"Flake stepping down reflects not only his dissatisfaction with what's going on in D.C. but also the reality that there was an emerging dissatisfaction among some of the Republican voters in Arizona," said Sides.
Flake's primary election was tightly contested in Arizona which is where Sides sees that dissatisfaction.
As for Corker's seat, Sides says Tennessee is a stronger Republican state.