The exit of Governor Walker from the Republican campaign for president is a sad moment for those of us who admired his campaign to liberate Wisconsin from the grip of state employees unions. But it also puts paid the notion, so often heard, that somehow Citizens United, the Supreme Court case that lifted many of the campaign finance limits put in place by the McCain-Feingold law, has tilted the tables in favor of the Republicans.

Only a few months ago, after all, Mr. Walter had emerged as the reported favorite of what is, if one believes the New York Times, the biggest, darkest money in the campaign, the Koch brothers. Yet a scant five months later and Mr. Walker is headed back to Wisconsin, citing difficulties raising money after his plunge in the polls. It would surprise us if Mr. Walker turns bitter about this reversal. He strikes us as a man of the markets.

Which are offering up a rich array of Republican candidates, even judging by the high standards of integrity and experience that were presented by Mr. Walker. He has already written himself into the history books with his battle against the labor unions crippling Wisconsin’s government (and economy). But he lacks for experience in foreign affairs, where he was eclipsed by other rising GOP stars like, say, Senator Rubio. Mr. Walker was less than fluent.

By our lights Mr. Walker made a number of mistakes, none greater than his tack to the right on immigration. This came in August in the wake of the demagoguery of Donald Trump. It was doubly disappointing to us, because we’ve been waiting for a GOP candidate to join the pro-life issue, on which Mr. Walker is so strong, with the pro-immigration issue. We dream of a candidate who will combine the laws of economics with the laws of the religious sages.

Both of them hold that more population is better, indeed necessary for human progress. And both sets of laws aren’t particular about the race, religion, national origin, or immigration status of human capital. We don’t mean to discount entirely the problems on the southern border. But the way to deal with them is through economic growth and capacious philosophical principles. Mr. Walker would have been an ideal candidate for that mission, which lends a poignance to his exit.

At his press conference this evening in Madison, after all, he spoke of how inspired he was a generation ago by Ronald Reagan and his “eternal optimism in the American people.” Reagan’s brother Neil had spoken of their Irish grandfather as “probably one of the early wetbacks,” having sneaked into America from Canada. Mr. Walker complained of the lack of the lack of optimism so far among the GOP field. But Mr. Walker forsook that very optimism with his turn against immigration. It was a mistake Reagan would not have made.