Writing in the Wall Street Journal's conservative opinion pages today, former Bush administration official Peter Wehner warns Republicans that embracing the Donald Trump-led birtherism that's currently sweeping conservative media will lead to “substantial damage both to their party and to American politics.”

From the WSJ [emphasis added]:

By focusing on Mr. Obama's birth certificate, Mr. Trump has garnered a lot of attention and some support. According to the latest CNN/Opinion Research Corporation survey, among Republicans he is now tied with Mike Huckabee as the most popular prospective GOP presidential nominee. If responsible Republicans don't speak out immediately against Mr. Trump's gambit, it will do substantial damage both to their party and to American politics.

...

When prominent figures in a party play footsie with peddlers of paranoia, the party suffers an erosion of credibility. While certain corners of a party's base might be energized by conspiracy theories, the majority of the electorate will be turned off by them. People are generally uneasy about political institutions that give a home to cranks.

There's more than a partisan cost to all this. Mr. Trump is succumbing to a pernicious temptation in American politics: not simply to disagree with political opponents, but to try to delegitimize them. The argument isn't simply that Mr. Obama is wrong on almost every public policy matter (which I believe he is). Rather, the argument is that his presidency is unconstitutional and that he is alien.