![Mitch McConnell](https://www.stephaniemiller.com/wp-content/uploads/2019/10/Mitch-McConnell-696x402.jpg)
WASHINGTON — The fight over the filibuster escalated in the Senate on Tuesday as Senator Mitch McConnell, the Republican leader, threatened harsh reprisals if Democrats moved to weaken it, a prospect that appeared increasingly likely as President Biden’s allies on Capitol Hill began building a public case for its elimination.