If America is faced with a national default because of Republican obstruction against raising the debt ceiling, in my opinion President Obama has authority under Article 4 of the 14th Amendment to the U.S. Constitution to act unilaterally if necessary to avoid a debt ceiling-induced default. If default is the only other option, the president should exercise this authority.
Unilateral presidential action to avoid a debt-ceiling default is the second worst option, and should be avoided if at all possible. Unilateral action sends an awful message to financial markets. While I believe such action would be reluctantly approved by a narrow Supreme Court majority after an inevitable challenge, judicial approval is not certain. Bipartisan and comprehensive budget, spending and revenue negotiations on all outstanding issues is a far more desirable outcome.