Indiana Gov. Mitch Daniels (Photo via Creative Commons).

Daniels was considered to be one of the frontrunners in the hotly-contested race for the GOP's nomination. Now, his resignation may disappoint many Republican supporters as it leaves more room in an already scattered field for a leader to emerge.

POLITICO reported:

The Daniels email, obtained by POLITICO, went out from Indiana GOP chief Eric Holcomb, a key Daniels adviser, soon after midnight, with the word "Urgent" in the subject line.

"The following is from Governor Mitch Daniels…." the email began.

“I hope this reaches you before the public news does," Daniels wrote. "If so, please respect my confidence for the short time until I can make it known to all."

"The counsel and encouragement I received from important citizens like you caused me to think very deeply about becoming a national candidate. In the end, I was able to resolve every competing consideration but one, but that, the interests and wishes of my family, is the most important consideration of all. If I have disappointed you, I will always be sorry."

Daniels has been noticeably hesitant to run due to his personal life ever since speculation began that he could win his party's nomination for 2012. 

From the Wall Street Journal:

Mr. Daniels, a two-term governor who had worked the administrations of both George W. Bush and Ronald Reagan, had often expressed concerns about the strains a national campaign would put on his wife and four adult daughters.

His decision to stay out of the race eliminates one of the last big Republicans still known to be eyeing a presidential campaign and rounds out a week that also saw two other well-known figures— Mike Huckabee and Donald Trump—take their names out of contention.

"If I have disappointed you, I will always be sorry," Mr. Daniels wrote. "If you feel that this was a non-courageous or unpatriotic decision, I understand and will not attempt to persuade you otherwise.  I only hope that you will accept my sincerity in the judgment I reached."

Daniels' absence leaves room for other major names to join the race--and may heighten pressure from Republican leaders on popular possible candidates to do so. So far, seven candidates have formally declared their candidacy, while former Minnesota Gov. Tim Pawlenty is expected to enter the race on Monday.