Presidential campaigns are not endeavors that treat laziness kindly, and all of the Republican contenders have packed and demanding schedules.

But over the course of his last White House run and through the first few months of this one, Romney has proven himself to be a particularly hardworking campaigner who never seems to lose focus, no matter the hour of the day. This tirelessness is a potentially significant asset that could pay major dividends as the candidates’ already taxing days become even more arduous.

“He’s the kind of guy who will see a hole in the schedule and instead of thinking ‘long lunch,’ he thinks of doing a campaign headquarters stop-by or a radio interview,” Ritter, who has been a fixture at Romney’s side since 2006, told RCP. “He can’t be stopped, and you almost have to trick him into not doing as much.”…

A hard-charger throughout his life in business and during his four political campaigns, the effects of Romney’s clean-living lifestyle are self-evident. As one aide put it, “He’s not the guy who gets a beer at the end of the night, so you save that hour-and-a-half.”