After recently waffling on his decision, Sen. Bob Corker will stick by his plan to retire.

Some U.S. senators and state party officials urged the Tennessee Republican to reconsider his decision to not run in November. Had he re-entered the race, it would have set up a potentially bitter primary election with Rep. Marsha Blackburn.

"Based on the outpouring of support, we spent the last few days doing our due diligence and a clear path for re-election was laid out," Corker's chief of staff Todd Womack said in a statement. "However, at the end of the day, the senator believes he made the right decision in September and will be leaving the Senate when his term expires at the end of 2018."

Politico first reported Corker's decision.

Blackburn is now considered the GOP frontrunner for the seat. Recent reports saying Corker could reconsider his retirement noted that some Tennessee Republicans privately worried Blackburn could be vulnerable to losing to a Democratic challenger, likely former Gov. Phil Bredesen.

Republicans aim to hold on to majorities in both chambers of Congress in November's elections. The GOP currently has a narrow 51-seat majority in the Senate.

Corker, the 65-year-old Senate Foreign Relations Committee chairman, is serving his second term in the chamber. A number of times last year, he offered candid criticism of President Donald Trump.

Blackburn has cast herself as a defender of the president.