Cory Booker’s presidential campaign launched with a flashy video, driven by a biography rooted in an optimism that should have found fertile soil in Iowa. He followed up with grind-it-out work on the ground in New Hampshire, where he racked up endorsements and packed venues. A speech on civil rights in South Carolina at an iconic African-American church tested by a massacre set him apart of a crowded field.

Yet, on Monday, Booker acknowledged the tough reality of 2020 and ended his presidential bid, saying he no longer saw a path to victory or had the cash to pave its way.

Booker was already set to be excluded from Tuesday night’s debate in Iowa, the last major gathering of contenders before the state’s Feb. 3 caucuses. Although he built a strong machine in Iowa, the latest Des Moines Register/ CNN poll released Friday put him at just 3% support — far short of the 15% threshold required to qualify for delegates.

Money has been a persistent problem for Booker, who after years of taking campaign cash from drug makers and their executives swore off that lucrative stream last year. The looming impeachment trial of President Donald Trump, where Booker is set to be a juror by virtue of his Senate seat, only complicated his prospects of finding the time and resources to break through.

“Our campaign has reached the point where we need more money to scale up and continue building a campaign that can win — money we don’t have, and money that is harder to raise because I won’t be on the next debate stage and because the urgent business of impeachment will rightly be keeping me in Washington,” Booker said in an email to supporters on Monday morning.

That looming impeachment business was the unknown challenge that wasn’t part of Booker’s original decision to run. Under expected Senate rules, Booker will be compelled to be at his Senate desk every afternoon, six days a week, for a trial of an unknown length. The trial, which could start as soon as this week, effectively sidelines Booker from the race. Running low on cash, flying private back and forth for morning or late-night rallies, just weren’t a viable options, and it’s hard to fill in the gaps with digital and broadcast ads.

Booker’s exit is the latest of a string of Democratic campaigns that began with so much promise but petered out before the election year began in earnest. A first-term Senator who faces re-election later this year, Booker joins the likes of Senators Kamala Harris and Kirsten Gillibrand in ending marquee races, in addition to former Housing and Urban Development Secretary Julian Castro, and Congressmen Tim Ryan, Eric Swalwell and Seth Moulton. Others who had momentary flashes of potential, like self-help author Marianne Williamson, also failed to gain traction in the race’s wide field.

Taken together, the winnowing of the Democratic field seems to run counter to what many expected when the cycle opened in the waning days of 2016 with the most diverse set of contenders in history. Today, the remaining frontrunners are all white. In Iowa, a cluster of 78-year-old Sen. Bernie Sanders, 70-year-old Sen. Elizabeth Warren, 37-year-old former South Bend, Ind., Mayor Pete Buttigieg and 77-year-old former Vice President Joe Biden are clustered atop the field in Iowa.

Polling gets more complicated elsewhere, but as Democrats repeatedly say that defeating Trump is more important than ideological choices, it seems they are seeking a candidate who more closely fits the mold of what previous nominees have looked and sounded like. Democrats may have also concluded that they weren’t ready to gamble with a Senator like Booker, whose national profile remains something of a blank page.

Nevertheless, Booker ran a dynamic campaign, recruiting some of the sharpest minds in Democratic politics and assembling a formidable machinery that, at every test, proved itself well. For a public speaker known to inspire, his debate performances weren’t universally stellar, but they were far superior to the too-often flat deliveries from the likes of Biden and Sanders.

Booker branded himself from the start as an optimistic, an early assessment of the Democratic field that was was spot-on. In the same Register/ CNN poll that showed only 3% backing for Booker, more than three-quarters of Democrats surveyed used the word “optimist” to describe themselves.

Ultimately, however, Booker found that more than optimism would be required to start piecing together sufficient delegations to the Democrats’ nominating convention in Milwaukee this summer. But the 50-year-old alumnus of Stanford, Oxford and Yale Law is hardly done with politics. Republicans aren’t seriously contesting his Senate seat this fall, so Booker will have time to travel and support Democrats. His endorsement will be a coveted commodity and he already has signaled that he will campaign for candidates up and down the ballot this year. His ability to blow the doors off venues large and small will prove invaluable for those lucky enough to win his backing.

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Write to Philip Elliott at philip.elliott@time.com.