Indiana Gov. Mike Pence, left, with presumptive Republican presidential nominee Donald Trump on July 12. (Tasos Katopodis/Agence France-Presse via Getty Images)

AS A conservative crusader, Mike Pence is an incongruous match for the ideologically flexible Donald Trump, who employed Twitter to name the Republican Indiana governor as his running mate Friday. Then again, anyone with a halfway respectable record in public office would have been an odd partner.

Perhaps Mr. Trump can relate to Mr. Pence’s time in show business: The governor was a radio host in the 1990s before winning election to the House in 2000. Though Mr. Pence is reportedly more easygoing than Mr. Trump, he has a bit of Mr. Trump’s penchant for the bizarre, as when he claimed in a magazine commentary that “smoking doesn’t kill.”

But it is likely that Mr. Trump chose Mr. Pence because the Hoosier is a more likeable version of Sen. Ted Cruz (R-Tex.), Mr. Trump’s vanquished adversary, whom Mr. Pence endorsed in the Indiana GOP primary. During his 12 years in Congress, Mr. Pence built up a reserve of credibility with movement conservatives and tea party types. He chaired the conservative Republican Study Committee and mounted one of the many right-wing campaigns to unseat Rep. John A. Boehner (Ohio) as the leader of House Republicans. Mr. Boehner later co-opted Mr. Pence by appointing him to the House leadership. Now Mr. Trump seems to be attempting a similar maneuver — neutralizing complaints from conservative true believers by bringing one of their own into the fold.

Mr. Pence’s policy record suggests he will indeed appeal to right-wing voters — but perhaps not many others. He waged war against Planned Parenthood while in Congress, saying in 2011 that he was willing to shut down the government in order to defund the organization. A staunch opponent of lesbian, gay, bisexual and transgender rights, he favored a constitutional amendment defining marriage as a union of a man and a woman. He pressed for a constitutional amendment that would cap federal spending at 20 percent of the economy, which would badly hamstring the government as baby boomers begin drawing retirement benefits. He also voted for and defended free-trade deals of the sort Mr. Trump has incorrectly blamed for hollowing out the economy.

Mr. Pence ran for governor as a fiscal rather than a social conservative, and he began his term by signing a large tax cut into law, which has made finding money for road construction a challenge. He has shown some practicality, taking federal money to expand Medicaid in his state under Obamacare as other GOP governors held out in irrational protest. His defining decision in Indianapolis, however, was signing into law a “religious freedom” bill that encouraged discrimination against LGBT people. He subsequently scaled the law back after a national uproar. Though this unnecessary foray into social issues hobbled him politically, he followed it up with a bill restricting abortions in Indiana. And while he condemned Mr. Trump’s proposal to ban Muslims from entering the United States, he also tried to suspend the settlement of Syrian refugees in his state.

Presumptive Republican presidential nominee Donald Trump picked Indiana Gov. Mike Pence (R) as his running mate. Here's what you need to know about Pence. (Peter Stevenson,Danielle Kunitz,Osman Malik/The Washington Post)

Mr. Pence appears to be executing his biggest mistake, by far, right now. He has called himself “a Christian, a conservative and a Republican, in that order.” But he has agreed to run on a ticket with an uncharitable man who habitually insults minorities, religions and vulnerable people, who wants to economically isolate the United States and who regularly displays his ignorance of the Constitution and policy. As he campaigns with Mr. Trump, Mr. Pence will have to add “hypocrite” to his list of labels.