The Indiana governor Mitch Daniels said yesterday he has decided not to seek the Republican presidential nomination because of family considerations, further narrowing the pool of candidates.
"The counsel and encouragement I received from important citizens like you caused me to think very deeply about becoming a national candidate," Mr Daniels said.
"In the end, I was able to resolve every competing consideration but one. That – the interests and wishes of my family – is the most important consideration of all," he said.
"If I have disappointed you, I will always be sorry."
Mr Daniels, a budget director in the administration of President George W Bush, had built a reputation as dedicated to reducing US debt, calling it the "red menace" that threatens to engulf the country.
His decision not to run removes a Republican heavyweight from a field that many political analysts view as weak. It well may enhance Mitt Romney's chances of becoming the Republican front-runner.
Mr Romney, a former Massachusetts governor, has been leading some early polls.
Meanwhile, Herman Cain, a former pizza-chain manager and Tea Party favourite, yesterday announced he would run for the presidency, despite never having held elective office.