I like Obama, he is great, but not ready to be President.
Lincoln barely had any elected experience at all when he became president.
Roosevelt was only governor of New York for four years before becoming president.
Eisenhower had no political experience whatsoever when he became president.
Kennedy had all of eight years in the Senate before becoming president, a lot of which he was absent for due to nearly dying on account of spinal surgery.
In a lot of ways presidents hailed as great have their talents determined by their character, not by their experience. You can be in the senate for fifty years or a governor for four terms and still not be presidential material. There's very little that a longer legislative career will aid you in becoming the chief executive official of the federal government.