A US army doctor faces up to three and a half years in jail after he was found guilty by a court martial yesterday of willfully missing a flight when deployed to Afghanistan because he doubts Barack Obama's right to be president. The trial of Lt Col Terrence Lakin was a rallying point for the "birther" movement, conspiracy theorists who believe Obama has fraudulently taken over the presidency and is not a "natural born citizen". Lakin posted a video on YouTube saying he had no choice "but the distasteful one of inviting my own court martial".

On Tuesday he pleaded guilty to one of the two charges – failing to follow an order to meet with a superior and failure to report for duty at Fort Campbell, Kentucky. He pleaded not guilty to the second count, relating to missing a flight to take him to the military base, but was convicted of that charge by the military jury.

Doubts about Obama's legitimacy to be president have swirled around the further lunatic fringes of conservatism and the right-wing blogosphere since he became a serious contender for the White House in 2008. Prominent "birthers", such as Orly Taitz, a California-based lawyer, claim that Obama was born in Kenya and that the birth certificate that Hawaiian officials possess showing that he was born in Honolulu on 4 August 1961 is a fake.

Lakin had hoped to turn his court martial into a trial over Obama's legitimacy, but in September a military judge ruled that the president's birth certificate was not an appropriate area for the court to consider.

At his hearing, Lakin told the jury that he had been "praying and soul searching. I believed there was a question that needs to be answered to ensure a valid chain of command. But I had asked every question, done everything else I could short of disobeying orders, without success."