Donald Trump is a force in the Republican presidential race. Two recent polls show him running second to Jeb Bush nationally. He’s also polling second in Iowa and New Hampshire. And his pronouncements are commanding attention, especially on Fox News, where he’s a popular presence.

Some of this is attributable to the fact that Mr. Trump is a genius at drawing the spotlight to himself. He thrives on social media. Democrats and the press are only too happy to highlight Mr. Trump’s stream of invective and outrageous utterances, including his claim that Mexico is purposely sending us drug dealers, rapists and carriers of infectious diseases.

To their credit, several Republican presidential candidates, including Rick Perry, Marco Rubio and Mr. Bush, have criticized Mr. Trump. Yet it’s also true that Mr. Trump has garnered respect from some of his fellow Republicans. According to Ted Cruz, Mr. Trump is “bold,” “brash” and “speaks the truth.” Rick Santorum likes it that he’s focused on “a very important issue for American workers and particularly, legal immigrants in this country.” An editorial in The Weekly Standard says Republicans can benefit from “a little touch of Trump” in rhetoric, attitude and bearing. According to Rush Limbaugh, Mr. Trump’s statements will “resonate” with many Americans.

They may. But they shouldn’t.

For starters, Mr. Trump, though he claims to be a conservative, is nothing of the sort. He’s barely even a Republican. For most of the last decade, he was a registered Democrat. It wasn’t that long ago that most of his political contributions went to Democrats, including Senators Harry Reid, Chuck Schumer and Hillary Clinton. Before he discovered his Republican roots, Mr. Trump favored a single-payer health care system and proposed a large “net worth tax” on wealthy individuals. He once declared himself “strongly pro-choice” and favored drug legalization. He is a vehement protectionist. Earlier this year he even accused Republicans running for president of “attacking” Social Security, Medicare and Medicaid. Why would conservatives find him the least bit appealing?