There’s a strong case for President Trump to face a Republican primary challenger. I know a thing or two about insurgencies. I entered Congress in 2011 as an insurgent Tea Party Republican. My goals were conservative and clear: restrain executive power and reduce the debt. Barack Obama was president then, and it was easy for us to rail against runaway spending and executive overreach.

Eight years later, Mr. Trump has increased the deficit more than $100 billion year over year — it’s now nearing $1 trillion — and we hear not a word of protest from my former Republican colleagues. He abuses the Constitution for his narcissistic trade war. In private, most congressional Republicans oppose the trade war, but they don’t say anything publicly. But think about this: Mr. Trump’s tariffs are a tax increase on middle-class Americans and are devastating to our farmers. That’s not a smart electoral strategy.

It’s one of the many reasons Mr. Trump is ripe for a primary challenger. In fact, it would buck the historical trend if he didn’t have one. More often than not, unpopular presidents face primary challengers.

Since leaving Congress in 2013, I’ve been the host of my own conservative talk radio show several hours a day, five days a week. The only time a majority of my conservative audience has noticeably broken with the president is when he signed the omnibus spending bill in 2017 that ballooned the deficit. Fiscal responsibility is an issue the American electorate cares about but that our elected officials disregard from the top down — including the Tea Party in the Trump era.