Biden is a creature of the Senate. Sanders is a creature of the campaign trail. Observing them back to back in these two settings helped clarify the choice before voters.

How voters decide what to make of this contrast — a candidate who seems bored by parliamentary tedium and loves the roar of his own crowds, and a candidate who thrives in the back rooms of Washington and in one-on-one settings with voters but struggles to excite the masses — could determine who wins the Democratic nomination.

Sanders rarely looks happy to be anywhere but he seemed particularly restless seated at his wooden desk in the center of the Democrats’ half of the room. He rarely took notes. His face was crimson. He fidgeted and seemed not to know what to do with his hands. He rubbed his temples. He removed his glasses and rubbed his entire face. At one point he simply stared off into the chamber and patted his head. One evening, as the proceedings went late he flipped through to the end of the packet of slides that the managers handed out, seemingly trying to determine when it would be over. He crossed his arms, leaned back in his chair, and stretched his six foot frame out until his legs nearly entered the space between Sens. Robert Menendez and Jack Reed in the row in front of him.

Sanders is 78, which makes him the eighth-oldest senator in a body that is known as a gerontocracy. As can be expected for a man of his age, during the trial Sanders took more breaks than anyone else I observed, testing the patience of Sen. Ben Cardin, who sat to his right and who Sanders had to navigate around each time he left their aisle.

During breaks in the trial the Senate becomes social. Surprising conversations break out: Norm Eisen, a lawyer working for the House managers, and Pat Cipollone, the White House counsel, warmly chatting; Sens. Chuck Grassley (R-Iowa) and Tom Carper (D-Del.) shaking hands for so long that they ended up just holding hands while they talked; Tim Kaine and John Cornyn sharing a laugh. To put it mildly, that’s not Sanders’ thing. He rarely engaged with his own colleagues, let alone the Republicans on the other side of the room. There are shared intimacies between senators that became clear as you watch them for hours. Mark Warner and Michael Bennet, who sit next to each other, frequently made each other giggle. Susan Collins and Lisa Murkowski, who share some doubts about the propriety of Trump’s behavior, occasionally exchanged knowing glances when bits of damning evidence were reviewed. Sanders did not partake in similar social interactions.

This is not exactly news. Sanders has always been a loner in the chamber. But what makes it so jarring to watch up close is that it was occuring just as his campaign has taken off. As the trial started, a trove of polling data told a new story about the presidential race. Sanders was gaining ground in Iowa and New Hampshire, he remained competitive in Nevada, and he was tied with Biden in California, the state with the most Democratic delegates. Elizabeth’s Warren’s steady tick downward had allowed Sanders to partially consolidate the left while Biden was still fighting off multiple challengers in the center. Washington Democrats, the least pro-Sanders constituency, who had mistakenly believed that Sanders was a spent force last year when the novelty — and polling surges — of newcomers Elizabeth Warren and Pete Buttigieg seized the media’s attention, suddenly had to grapple with the fact that he could win the first three states.

But at least from the gallery, there was no sense that Sanders had returned to the Senate a conquering hero. The chamber was filled with rivals who were struggling to catch Sanders or who had already dropped out of the race: Bennet, Amy Klobuchar, Cory Booker, Kirsten Gillibrand, Kamala Harris. When Sanders turned his head a few degrees to the left he had a line of sight to Elizabeth Warren, who had recently accused him of calling her a liar on national TV.

In Des Moines Sanders is a rockstar. In Washington he sat alone and silent among the people he could soon lead, surely knowing he is not their choice. When he looked around him, a few desks to the left or right, he saw the five senators who have endorsed other candidates in the race. The only Senate colleague to back him is Pat Leahy, who is also from Vermont.

“It’s not uncommon for a legislator who is a loner or a maverick or otherwise does not work within existing structures to be more well liked by the general public,” said Sen. Brian Schatz, who sits directly behind Sanders and doesn’t plan on endorsing anyone in the primary. The sausage-making process almost always makes longtime effective legislators unpopular.

Schatz added some nuance to the view of Sanders as purely a curmudgeon. “He’s not a backslapper type, but neither is he anti-social,” Schatz said. “He can bring himself to be phony with people and he’s got a shyness about him at the interpersonal level. But he’s not the natural born politician from a Robert Caro book.”

This is now the essence of the Democratic fight: a race defined by a maverick socialist who values uncompromising stands across a range of issues versus a party stalwart who seeks a return to a type of Washington consensus policy-making that may no longer exist (if it ever did).

On Wednesday night, after watching the Senate trial for a few days, I watched Biden give his familiar stump speech before a modest crowd in Council Bluffs. Sanders was still stuck in Washington and the distance between the two candidates was never starker. Biden was introduced by a firefighter from the union that has endorsed him, and that promoted Biden to begin his remarks by recalling three awful events in his life where firefighters saved him or members of his family. They extracted two of his children from the wrecked car crash that killed his first wife and baby in late 1972. They helped get him to the hospital for emergency brain surgery when he had an aneurysm in 1988. And in 2004, when lightning struck Biden’s Delaware home and started a fire in the kitchen, firefighters quickly contained the blaze. Unlike Sanders, Biden is all human connection and personal story-telling.

Though he’s adjusted the pitch somewhat to respond to critics, the heart of Biden’s speech still includes a paean to the old Senate where relationships matter more than anything else and what’s most important is to never, as he puts it, question a colleague’s motives, only their judgment. Biden even quoted David Brooks about restoring America’s “moral fabric.” On Wednesday he added a specific criticism about the dangers of attacking a fellow legislator as being, for example, “in the pocket of” an industry. Once you get personal, he insisted, the deals can’t get done.

This is the flip side of Sanders’s flaw. Sanders eschews relationships and deal making to a fault, while Biden fetishizes them to a fault. Sanders, according to Hillary Clinton’s recent harsh assessment, is someone that “nobody likes” and “nobody wants to work with” in the Senate, but in Iowa he has raucous crowds and actual rock stars campaigning for him. Biden is a beloved figure among Democrats in the Senate and has trouble rousing an audience in Iowa.

In the midst of an impeachment trial that is about a plot to define Biden as personally corrupt — in the pocket of big Ukraine! — Biden’s argument about relationships sounded hollow. He seems to recognize this. In Council Bluffs, Biden quickly pivoted to a perhaps more effective pitch about how the Republican Party was trying to destroy him because they believed he could beat Trump.

“They’re trying to smear me to stop me,” he said. This time the crowd applauded.