There are lots of reasons why people believe, or claim to believe, that Barack Obama isn't a "natural born citizen." Some may have racist motives. Some may be grasping for any stick to beat a Democratic president. Some might just be finger-twirling, lip-bibbling crazy.
And some, likely not true believers, may be trying to cast doubt on the legitimacy of Obama's presidency for a much simpler reason:
George W. Bush was not elected president of the United States.
While it might take some effort to discredit public health documents and newspaper announcements from Hawaii, or to conflate a father's nationality into a Manchurian candidate fantasy, the illegitimacy of the Bush presidency is a matter of record.
Five justices of the Supreme Court overruled the popular and electoral votes of the American electorate, claiming that actually determining the true winner of the 2000 election would "irreparably harm" the result that they themselves chose.
And they did it with all of America watching on live TV.
Bush was a lot of different kinds of president. He was a War President, a Terrorism President, a Worst President, a Legacy Hire President, the Most Vacated President. But from the very beginning, he was an Asterisk President.
The entire misadventure that was the Bush era began with the humiliation of his ascent, not through the Will of the People, but the whims of five people, whose reasoning was so spurious that they themselves declared no one could ever use it again. Not since 1876, when the House overrode the will of the voters and seated electors for "His Fraudulency" Rutherford B. Hayes, had such an patent default been sent to the White House.
And history has shown that Republicans, when faced with their own shameful desecration of the Constitution, turn to the first defense of the five-year-old: "They did it, too!"
Got a president who resigned office, one step ahead of impeachment? Quick, find a reason to impeach one of theirs. Got a candidate who bailed on his military service? Better discredit your war hero opponent's.
Got a president who couldn't get legitimately elected even when you cheated? Better find a way to discredit theirs.
I have no idea why someone would take the birther business seriously. But if the Mombasa Manchurian fantasy can cheapen Obama's presidency the way the Selection of 2000 tainted Junior from the jump, well, by golly, it's good enough for the Republicans.