WASHINGTON — Hours after Jimmy Kimmel unleashed a monologue attacking the latest bill that would undo much of the Affordable Care Act, two of the bill’s authors spent Wednesday morning defending the legislation against the late-night host, who in recent months has become an unlikely — and increasingly impassioned — critic.

Mr. Kimmel, who has closely watched the Republican effort to strip down health care since his newborn son had open-heart surgery, targeted Senator Bill Cassidy of Louisiana in particular. In what was only the latest instance of the ever-blurring line between late-night laughs and politics, Mr. Kimmel delivered an earnest monologue on Tuesday evening on “Jimmy Kimmel Live!,” accusing the senator of failing to deliver on several key issues, including lowering premiums, expanding coverage, banning lifetime caps and not discriminating based on pre-existing conditions.

“This guy, Bill Cassidy, he just lied right to my face,” Mr. Kimmel said. “Guess what? The new bill does none of those things.”