“There was an understanding with the Democrats,” said Hamilton professor Dennis Gilbert, who worked for Sanders’ campaign that year doing polling and writing policy papers. “They realized that if he was running, they couldn’t win.”

“For a lot of Democrats, Bernie was our candidate,” said Poirier, the Democrat who finished behind Sanders in ’88. “By 1990, he had pretty much won the support of most elected Democrats.”

He was their only real option.

Welch endorsed him, he said, “because he had the best chance of winning.”

“He basically expropriated their base of voters,” said Fred Bailey, a Republican city councilman during Sanders’ time as mayor. “They couldn’t out-Bernie Bernie.”

The ’90 race was the beginning of the rest of Sanders’ political life. Smith, the Republican, seeing Sanders’ support swell, got desperate and used debates and ads to hit him for his socialist philosophies and also for his anti-Democratic Party rants. Smith plucked from Vermont Affairs the “ideologically bankrupt” comment. It backfired. People in Vermont recoiled at Smith’s tactics, and Sanders won in a landslide. And Sandoval, the Democrat? She didn’t get 5 percent—she got 3.

It was official. In Vermont, in Sanders’ races, the second major party was … Bernie.

***

“I.”

That letter next to Sanders’ name is more than a political classification. It’s a personal declaration.

He was, when he arrived in Washington, the only one of the 535 members of Congress who didn’t identify as either a Democrat or a Republican.

“I am extremely proud to be an independent,” he told the Associated Press seven months into his congressional career. “The fact that I am not a Democrat gives me the freedom to speak out on the floor of the House, to vote against both the Democratic and Republican proposals.”

The flip side at first was this: “He screams and hollers,” Rep. Joe Moakley (D-Mass.) said to the AP at the time, “but he is all alone.” Rep. Bill Richardson (D-N.M.) called Sanders “a homeless waif.” Said Rep. Barney Frank, in ’91: “Bernie alienates his natural allies. His holier-than-thou attitude—saying in a very loud voice he is smarter than everyone else and purer than everyone else—really undercuts his effectiveness.”

Today, looking back, colleagues in interviews with Politico recalled questions from party elders about whether to allow Sanders to sit on committees. Sanders mentioned as much at a lunch with Senate Democrats last month, telling them it was like wandering around “in the desert” when he first came to the House. While Sanders formally was part of the House Democratic Caucus, said Sen. Sherrod Brown of Ohio, who served with Sanders in the House, “he was not really a member of the caucus.”

It eventually worked out when the Democratic speaker, Tom Foley, reached the conclusion that it was better to expand his party’s membership than shrink it. That became even more important in ‘94, when the Newt Gingrich-led Republican takeover meant the Democrats needed every potential vote they could get. Sanders served on committees dealing with financial services issues and government operations, and he was extremely active in pushing amendments on the House floor, periodically teaming up with the likes of libertarian-minded Ron Paul.

“He would often get amendments on the floor—and call them tripartite,” Brown said. “He passed a lot of amendments in a very conservative Congress.”

Sanders spent a decade and a half in the House. He was seldom even challenged by a Democrat in Vermont.

He won the Democratic primary for the 2006 Senate race as a write-in candidate — there was no serious opposition — but he declined to accept the nomination before going on to beat his Republican opponent by 33 percentage points. The Senate was a better fit.

“The Senate,” one of his Democratic friends told Politico, “was the first time he’s ever been part of a Democratic family.”

The Democratic Senatorial Campaign Committee, led by New York’s Chuck Schumer, quickly got behind Sanders when he ran, and Nevada’s Harry Reid happily welcomed him to the Senate Democratic Caucus once he won. In December of that year, a month after his election, Ted Kennedy invited Sanders and the rest of the Democrats on the Senate’s Health, Education and Labor and Pensions Committee to an intimate dinner at his Washington home. Also in attendance? Barack Obama. And Hillary Clinton.

This embrace of Sanders was about politics, too: Democrats wanted to increase their numbers, and they needed Sanders to caucus with them to help win back the Senate majority. The move paid off for both sides. Sanders climbed the ladder: In the last Congress, he was the chairman of the Veterans' Affairs Committee; now, he is the top Democrat on the Budget Committee.

After the 2010 election, Obama cut a deal with the Republicans to extend the George W. Bush-era tax cuts, eliciting outrage from the left. Sanders channeled that anger, unleashing an 8½-hour filibuster. He said in the speech many of the things he had been saying since his populist, rusted-Volkswagen Liberty Union days in the ’70s, since political types in Vermont dismissed him as a no-shot gadfly—only now he was doing it on the Senate floor. “This,” he said, his accent immutably Brooklyn, “is a transfer of wealth. It is Robin Hood in reverse. We are taking from the middle class and working families, and we are giving it to the wealthiest people in the country.”

Sanders speaks to reporters about his position on the tax compromise in December 2010 on Capitol Hill in Washington. | AP Photo

Last year, in the midst of the Veterans Affairs scandal, Sanders worked with House and Senate Republicans to overhaul the agency, showing a dose of bipartisanship—something that hasn’t been a dominant part of his legislative repertoire.

He is better known for being mostly an ideological purist from the left—advocating for a single-payer, Medicare-for-all-type health care system, railing against Obama’s trade agenda.

“I think it was success trumped all,” Welch said. “He’s popular with voters. That’s a reality. His popularity really mended fences.”

Even some of his critics acknowledge how close he’s grown to Senate Democrats.

“We are a tight-knit group—we like one another,” said Sen. Claire McCaskill (D-Mo.), who nonetheless is a Clinton supporter, in part because she isn’t sold on Sanders’ eventual “electability.”

One reason analysts and strategists doubt his long-term viability: “democratic socialist.” Another: his record of bashing Democrats. The longer he runs, the better he does, the more the comments will be used to attack him.

In a second interview with Sanders in the Capitol, he talked more with Politico about his relationship, and his tussles, with Democrats.

“By definition, when I was elected mayor of the city of Burlington, I defeated Democrats,” he said with a chuckle. He talked about the importance of the ’88 race. “Since that time, in Vermont, I’ve had a lot of support from the Democrats.

“I was the first independent elected in 40 years, and that caused some confusion,” he continued. “And there were some conservative Democrats who were not enthusiastic about me being in the Democratic Caucus. But that worked itself out over a couple weeks.

“I’ve supported the Democratic candidates for president,” he added. “I think the relationship is pretty positive.”

“I think in many ways he’s become a Democrat in all but name,” said Eric Davis, a political science professor at Vermont’s Middlebury College.

“Even so," said Judy Stephany, a Burlington Democrat who lost to Sanders in the mayoral election of ‘83, “if you want to go back to 1981, ’85, ’87, even the late ’80s, this was not a man who liked either party—nor did he call himself a progressive. He has been very steadfast in maintaining his independence.”

It remains to be seen if or how much that will hurt him in the coming months.

“I think that probably goes against him,” said Rep. Elliot Engel (D-N.Y.), who served with Sanders in the House—and who back in ’96 even advised a Democrat in Burlington not to run against Sanders. But now? “The nominee of the Democratic Party you would think would be a Democrat.” He paused. “In fairness to Bernie, he always caucused with the Democrats. He’s a socialist in name … but in terms of political affiliation, he’s just like any other Democrat.”

Why then, Politico asked, why not just say so? Why not become a Democrat? Especially now.

Sanders wouldn’t say.

“I’m running for the Democratic nomination,” he said. He assured he would meet “all the regulations and requirements.” “I look forward to doing that,” he said. Another non-answer.

The real answer courses through his career. “Ideologically bankrupt …” “You don’t change the system …” “Why should we work …?” Many people, in Washington and Vermont, Sanders supporters and not, say that since his earliest, more radical start, the tenor of his rhetoric has changed. But the essence of his beliefs, the core of who he’s been and who he is—that unapologetic, almost confrontational “I”—has not.

“In real terms,” he told a reporter doing an interview for Playboy, “what the Democratic campaign program is about is: We’re pretty bad, but they’re worse, vote for us. That’s true: We’re pretty bad, but the Republicans are worse, and that’s the reason you should vote for Democrats.”

“I am not a Democrat,” he told the Progressive, “because the Democratic Party does not represent, and has not for many years, the interests of my constituency, which is primarily working families, middle-class people and low-income people.”

Sanders didn’t say those things in the ’70s or the ’80s. He said those things not even two years ago.