McManus: Welcome to the Democratic Party, Bernie

After 44 years in politics, Bernie Sanders has finally taken the plunge. At long last he's a regular Democrat.

Of course, he doesn't quite want to admit it. “I was elected as an independent, so I'll stay (in the Senate) two more years as an independent,” he told reporters at the Democratic convention last week.

Indeed, he still wishes it were possible to organize an independent leftist party in the United States, the way European countries do. “We don't have that,” he said a little mournfully.

But after decades of agitation as an outsider, he's decided the best way to pursue his “political revolution” is to campaign for a ticket he doesn't like very much. And that's pretty much the definition of a party regular: someone who works for candidates he disagrees with - as long as they carry the right label and the disagreements aren't too wide.

Sanders didn't merely endorse Hillary Clinton in his stem-winding speech at the convention; he endorsed her wholeheartedly.

“I am proud to stand with Hillary Clinton,” he said. “Any objective observer will conclude that - based on her ideas and her leadership - Hillary Clinton must become the next president of the United States.”

He pleaded with his die-hard supporters to join him, and he promised to work not only for the presidential ticket, but also for Democrats running for Congress, state legislatures and local offices.

“I support Democrats,” he said.

His “main role,” he added, will be “to make the Democratic Party a 50-state party.”

Clinton campaign chairman John Podesta said he's delighted that Sanders is on the team. “He can go campaign for us in any of the battleground states,” Podesta said, noting that Sanders had energized millions of young voters who still haven't warmed to the nominee. Sanders could be especially helpful in the swing states he won during the primaries, such as New Hampshire and Wisconsin.

Sanders has supported Democratic presidential candidates before, going back to Walter Mondale in 1984. But that was mostly a low-key affair in his home state of Vermont. This time, he's talking about a much more visible national role, closely coordinated with Clinton's campaign.

Sanders is also launching a new organization, Our Revolution, to continue pushing the Democratic Party to the left. But it'll be a little less revolutionary than it sounds. Its heart will be a very traditional political activity: fundraising. That's right: Sanders will put his enormous list of donors to work for Democrats - OK, progressive Democrats - at every level around the country.

For decades, leftists in American politics have had a prickly relationship with the Democrats - sometimes working within the party (as in the 1972 George McGovern campaign), sometimes breaking with it, sometimes forming third parties or independent organizing committees.

Sanders is a part of that history; when he began running for office, in 1972, it was as a candidate of Vermont's almost-forgotten Liberty Union Party. He regularly denounced Democrats as sellouts to a corrupt political system. Even as a candidate for the Democratic presidential nomination, he was initially reluctant to embrace the party label.

But Sanders isn't really betraying his past, or his supporters. He's willing to join the dark side now because it's not so dark (to progressives) anymore; in fact, it's downright hospitable for small-d democratic socialists.

Democratic voters aren't what they used to be: In 2000, the Pew Research Center reported recently, only 27 percent of Democratic voters described themselves as liberal; now that number is 41 percent.

Case in point: The first President Clinton, Bill, was a champion of business-friendly free trade agreements like NAFTA. If there's a second President Clinton, she'll be a self-proclaimed skeptic on trade.

In other words, just as the Republican Party has become more conservative, so too have the Democrats become more progressive. (Sanders' success is proof of that.)

The party apparatus isn't what it used to be, either. Sanders was right when he said the Democratic Party platform is the most progressive one ever. He and his supporters were able to push Clinton to the left on several major issues: a pledge to make public universities tuition-free for most students, a promise to raise Social Security benefits and opposition to the current version of President Barack Obama's proposed trade agreement with Asia, the Trans-Pacific Partnership.

Sanders didn't win the nomination; he didn't even come very close. But over the course of the competition, he became a Democrat - functionally, if not yet in his own self-image. More important, the Democratic Party became more like him.

Doyle McManus is a columnist for the Los Angeles Times.