NEW : Republicans reject warnings of catastrophe without a higher debt ceiling . Conservative senator breaks from his previous pledge of no tax increase . Comment: Coburn is one of six senators in bipartisan talks on deficit reduction .
NEW : Republicans reject warnings of catastrophe without a higher debt ceiling . Conservative senator breaks from his previous pledge of no tax increase . Tax reform would lower rates and end loopholes , Sen. Coburn says . Coburn is one of six senators in bipartisan talks on deficit reduction .