U.S. Sen. Jeff Merkley (D-Ore.) spent the better part of 2018 raising his political profile and teasing a run for the presidency.

The speculation about a Merkley presidential run began as early as 2017, in part because he was the lone senator to support U.S. Sen. Bernie Sanders (I-Vt.) in the 2016 Democratic presidential primary.

That support, after the Democrats'  nominee, Hillary Clinton, lost to Republican Donald Trump, gave Merkley a leg up on other candidates hoping to harness the enthusiasm Sanders generated. CNN anointed Merkley a potential successor at the head of the Sanders wing of the party, although Sanders has yet to rule himself out of another run.

Merkley gained national attention last June, when officials at a Texas detention center for child immigrants responded to his unannounced visit with a call to police. A Facebook live video of the event went viral.

That same month he told the New York Times he was "exploring the possibility" of a presidential run.

Merkley followed up last fall with more deliberate steps toward joining the crowd of Democrats contending for the presidency: he raised money for candidates in Iowa and New Hampshire; he hired staff in those states.

He also informally asked Oregon legislators to consider changing an existing law, so that he could be on the ballot for two offices—for U.S. Senate and the presidency—in the same year.

But then there was a first stumble: he didn't make headway in Salem, and Tweeted out a response that was far from the steely ambition that usually characterizes a presidential candidate.

"It doesn't appear that there is a consensus to make this move at this time and I'm completely fine with that," he wrote. "Our leaders in Salem have plenty of important issues to build consensus around."

And as the crowd of Democrats entering the race has swelled, Merkley, already a long shot candidate from a small state, has been shunted to the side in national press coverage of leading contenders.

And he didn't get the kind of reception in a visit to Iowa last month that would help him break out of the crowd. "Atmospheric note: Crowd was friendly but not entirely silent during Merkley," Washington Post reporter Dave Weigel Tweeted at a Dec. 20 event.

The New York Times on Dec. 29 ran a story that mentioned a dozen candidates for the Democratic presidential nomination. None was the junior senator from Oregon.

A couple days later, Merkley pushed pause on the speculation that he will seek the presidency.

"You would really have to build a vast operation to be competitive given the design of our primary system," Merkley told Oregon Public Broadcasting on Jan. 2, "and that would require an all-out effort. And so it's balancing that effort against putting all my efforts in through the Senate."

Again, this week, when the website Five Thirty-Eight put together a list of 10 leading potential presidential candidates for 2020, Merkley didn't make the cut.

Merkley told OPB that he's aiming for a decision by the end of March on whether he'll run. In the meantime, the crowd of Democrats running for president is growing by the day.