Several GOP members of the upper chamber — most of them advanced in age — have struggled to acclimate to the style and agenda of President Donald Trump.
And some have drifted from their party’s base — a base increasingly willing to back insurgent challenges against incumbents. The prospect of serious electoral mortality appeared to play a role in Corker’s decision. A recent poll found the Tennessee senator trailing potential insurgent GOP challenger Joe Carr.
And earlier this week, Roy Moore in Alabama actually did knock off an incumbent. Moore, a former state supreme court judge, defeated Sen. Luther Strange (R-Ala.) in Tuesday's special election. Strange had been appointed by a governor tainted with scandal and then vigorously defended by Senate Majority Leader Mitch McConnell.
Other factors including health concerns and gubernatorial aspirations also could drive the next GOP exits from the Senate. The possible retirees are among the most influential in the chamber: Including Corker, there are four committee chairmen and a member of GOP leadership.
Here are the six of the most likely to consider retirement before the 2018 and 2020 elections.
Sen. Jeff Flake (R-Ariz.) is up for his first re-election in 2018 and is possibly the most endangered GOP incumbent in 2018.
Flake, first elected to the House of Representatives in 2000, has all but dared conservatives and Trump loyalists to pull him from office with his frequent criticisms of the president and his agenda. Trump is popular in Arizona with Republicans, and Flake was one of the Senate's original "NeverTrumpers."
Flake, elected to the Senate in 2012, is currently trailing his Republican primary opponent, former State Sen. Kelli Ward, by 25 points, according to an August survey conducted by JMC Analytics and Polling. His approval ratings are also anemic, with 37 percent of Arizona voters approving of Flake's job, and 45 percent disapproving, according to an August poll by Morning Consult.
Flake isn't likely to bow out of his reelection bid but does appear in danger of suffering a humiliating primary defeat.