From the statement: "I want to clarify that my Administration will not authorize the indefinite military detention without trial of American citizens. Indeed, I believe that doing so would break with our most important traditions and values as a Nation. My Administration will interpret section 1021 in a manner that ensures that any detention it authorizes complies with the Constitution, the laws of war, and all other applicable law."
Why should Obama expect anyone to trust him? First of all, he's a politician, and politicians rarely keep their promises to ordinary people. Second of all, Obama in particular has a less than stellar record of keeping promises. For one thing, he promised during his campaign to end "politics as usual in Washington," but in his first year in office engineered a Machiavellian vote-buying scheme in order to get Obamacare through Congress. Oh, and he also promised not to use signing statements to circumnavigate legislation signed into law.