BATON ROUGE, La. — When it comes to Bill Cassidy, most everyone in Louisiana politics — supporters and detractors alike — feels bad for the senator.

For his 20 years in politics, he’s mostly been a doctor in lawmaker’s clothing: evidence-obsessed, carefully calculating the right policy prescriptions for the issues before him, according to more than a dozen people who’ve worked with or for him. Those traits, along with his firsthand knowledge of America’s health care system, made him a respected leader on the subject in the Capitol.

He could be at the zenith of his power: He’s leading the Senate committee that oversees health policy, with Republicans in charge across the federal government and health care affordability emerging as the top political issue ahead of the midterm elections. He’s led the GOP in health reform plans for nearly a decade, and his recent policy proposals are, at times, more Trump-aligned than those of many colleagues.

Instead, Cassidy, 68, has increasingly set aside his health policy credentials in favor of proving his MAGA bona fides. He’s facing a tooth-and-nail primary fight on May 16 to keep his Senate seat, with President Trump and the politically ascendant Make American Healthy Again movement endorsing one of his challengers.