Sen. Mitch McConnell was a generational force for the Republican Party — using procedural tactics and political will to stymie much of former President Barack Obama’s agenda, hand President Donald Trump key first-term political victories and deliver a 6-3 conservative Supreme Court majority.

President Trump added fuel to the fire in his feud with former Senate Republican Leader Mitch McConnell, claiming the longtime Kentucky senator lacked the mental sharpness to shepherd GOP members in the upper chamber.

President Donald Trump seems to have questioned a well-documented part of Sen. Mitch McConnell’s life — his childhood battle with polio

McConnell cast the lone Republican “no” vote against Robert F. Kennedy Jr., just a day after he cast the only GOP vote for Tulsi Gabbard.

The former top Senate Republican was the lone GOP vote against Robert F. Kennedy Jr. 's confirmation to lead the Department of Health and Human Services. A polio survivor, McConnell had previously spoken out against the anti-vax nominee. On Thursday, the president condemned McConnell, saying the senator "let the Republican Party go to hell."

Robert F. Kennedy Jr. was officially confirmed as secretary of Health and Human Services Thursday with Sen. Mitch McConnell being the only Republican to vote against his confirmation. Meanwhile, former WWE CEO Linda McMahon took questions from the Senate Thursday in her bid to lead the Department of Education.

As most Republicans have fallen in line with Trump's agenda, one former ally is pushing back and testing his own power in Washington in the process.