WASHINGTON -- It's the most prominent position at the Capitol that comes with almost no power at all.

There's a nearly complete disconnect between its high visibility and its low impact on what Congress gets done. The vaunted title guarantees hours of free uninterrupted national TV exposure, but the job remains so thankless that many publicity-hungry politicians have to be dragooned into taking their turn.

For senators, in other words, being the presiding officer is the ultimate sinecure. That's because in the modern Senate, virtually all power to shape and pace floor debate is controlled by party leaders _ and almost all procedural showdowns are mediated by precedents as interpreted by parliamentarians.

So the highfalutin title "acting president pro tempore" is accompanied by minimal responsibility and even less labor. It's a patronage post coveted by none, foisted upon many and grudgingly appreciated only by some.

Its hollowness was highlighted with some irony last week when Marco Rubio of Florida -- who spent so much of the past year vivaciously pursuing the presidency -- presided robotically over several hours of speech making punctuated by long quorum calls, with essentially no legislative business getting done. It was the third time he had quietly assumed the chair since his time in the center of the national political hubbub came to an end.

As a Republican with less than a full six-year term under his belt, Rubio is obligated to mark time as the presiding officer under a byzantine handshake arrangement among senators that's rigorously monitored by the leadership. The dozen genuine freshmen elected in 2014 have to put in the most hours. Eighteen others, who were elected in 2010 or 2012 but only gained majority status last year, can get away with doing less.

All will be done with their obligations once they've won a second term -- or the Democrats win control of the Senate and are obligated to take on the task.

To be sure, a handful of senators say they genuinely appreciate time in the chair, generally doled out in hourlong increments. They learn aspects of parliamentary procedure that might come in handy someday. They come to appreciate the operating styles, rhetorical skills and parochial concerns of their colleagues.

And the podium shields them from the intrusions of lobbyists, staffers and fundraising consultants _ so they can get plenty of work done between occasional tapping of the tiny, hourglass-shaped ivory gavel, recognizing the next speaker or announcing the results of a roll call.

The prohibition against smartphones on the dais is honored in the breech, with many presiding officers sneaking peaks at their emails in between reading briefing papers and editing speeches.

"Politics is a relational business, and sitting up there gives you great insights," says Dan Coats of Indiana, who volunteers for one shift a week. "I've learned a lot from the body language among my fellow Republicans and between them and the Democrats -- the cold stares and phantom daggers."

"Sometimes, it's important to just stop and realize that only a very few number of people in all our history have been able to have this view," says Bill Cassidy of Louisiana, the first Republican elected in 2014 to notch more than 100 hours in the chair.

"You get a lot of uninterrupted study time," says another freshmen who has met that mark, Joni Ernst of Iowa.

That milestone entitled them to the only tangible reward that comes from loyal service as presiding officer, a Golden Gavel Award -- the mallet is actually made of brass -- and a public "thank you" from the longest-tenured senator in the majority, who as president pro tem is the default presiding officer.

Vice presidents, who are also presidents of the Senate under the Constitution, presided regularly until Richard Nixon got the job in 1953 and decided he had better things to do. Now vice presidents show up only to cast tie-breaking votes or to announce the passage of momentous legislation.

James Lankford of Oklahoma also earned a gavel this spring. And two others, Tom Cotton of Arkansas and Cory Gardner of Colorado, are on course to pass the 100-hour mark around Memorial Day.

Precisely how much time each senator has devoted to the task is a closely guarded secret, for fear that some Republicans might be embarrassed by evidence they've been shirking their duty.

But a rough estimate can be gleaned by determining, through a Congressional Record search, how frequently each senator has assumed the chair. And the differences are stark. Eight of the 12 freshmen have held the gavel on at least a quarter of the days the Senate has met since January 2015. At the other extreme, West Virginia's Shelley Moore Capito has done her duty just 20 times, thanks to a savvy decision to sign up for Friday mornings, by which time the Senate has routinely recessed for the weekend.

(Even the Senate's remaining GOP presidential aspirant, Ted Cruz of Texas, has taken on the task more often, although not once in the past five months.)

The others at the low end are all nearing the conclusions of their first terms. Bringing up the rear are Roy Blunt of Missouri, who has presided only once, and Jerry Moran of Kansas, who has never presided at all. Both have been exempted because of positions in the leadership, Moran the chairman of the campaign committee that won back the Senate for his party and Blunt the GOP Conference secretary since his third year in office.

Asked if he was glad his position in the party hierarchy brought along a waiver from the presiding officer's chores, Blunt's reply was a succinct and emphatic "Yes!"