WASHINGTON—In 2017, when President Trump was fresh in his first term, then-Senate Majority Leader Mitch McConnell was asked by a student on a class trip what he thought of the new commander in chief.

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.

Mitch McConnell is pushing back against President Trump’s most controversial nominees, becoming an unlikely — and sometimes lonely — face of Republican resistance.

It’s the latest rhetorical assault from the president on the former GOP leader, who has voted against three of his nominations.

President Donald Trump seemed to question a well-documented part of Sen. Mitch McConnell's life — his childhood battle with polio — after the Kentucky Republican opposed vaccine skeptic Robert F. Kennedy Jr.'s confirmation Thursday as the nation's top health official.

The GOP's recent and longest-serving Senate party leader has stood in opposition to his conference multiple times, demonstrating the party’s significant transformation in the age of Trump.

The Senate approved Kennedy to lead the Department of Health and Human Services on a largely party line vote on Thursday.