So Rubio hasn’t been voting on the Senate floor, and he hasn’t been spending day after day after day in the early primary states, either. What is he doing? “He’s working his tail off,” says Rubio spokesman Alex Conant. “It’s possible that somebody is working as hard as Marco, but nobody’s working harder.”

It appears what Rubio is doing most of the time is fundraising. The recent report that he raised $5.7 million in the third quarter — not an impressive sum compared to Carson, Bush, and Cruz — suggests that Rubio has a long way to go to run a first-tier campaign. So this week, for example, Rubio was on an early Wednesday morning flight from Washington to Houston, and then, after a three-hour stay, on another flight to Dallas, and Thursday on a flight to California, all for fundraising before flying to South Carolina on Friday. All of the flights are commercial, which saves money and allows the campaign to present itself to donors as a lean-and-mean operation. But it takes a lot of the candidate’s time, and wears him out, too.

Of course, other candidates have heavy fundraising demands and manage to spend more time in the early states. And the senators among them spent more time in the Senate. Ted Cruz, for example, raised more money, spent more time in the early states, and was present for more Senate votes than Rubio.