New York City Mayor Michael Bloomberg said he won’t run for president in 2012 and declined to endorse the potential candidacy of Donald Trump, one of his constituents. Speaking on “Fox News Sunday,” Mr. Bloomberg called Mr. Trump a friend and “New York icon.” But he criticized the idea of questioning whether President Barack Obama was born in the U.S., an issue that Mr. Trump has pressed. “The president was born here,” Mr. Bloomberg said. “I think the Republicans are making a terrible mistake in making this a big issue.” Mr. Bloomberg said that if Republicans don’t address larger issues...