President Obama has criticised Republican challenger Mitt Romney over his inconsistency on serious issues such as tax cuts and defense spending.
The Democrat was speaking to supporters in Iowa and added that Romney's inconsistencies lead to questions over his trustworthiness.
He said: "We joke about Romnesia but all of this speaks to something really important and that is the issue of trust. There is no more serious issue on a presidential campaign than trust. Trust matters."
The President went on to say that he could be trusted: "You know that I say what I mean and I mean what I say."
The latest polls show that Obama has pulled slightly ahead of Romney in the battle for the presidency, but the race remains more or less tied with just under two weeks to go until the election on November 6.