When Massachusetts Democrat Elizabeth Warren and the rest of the 2013 class of liberal senators start work this month, they'll have to do more than figure out the byzantine ways of getting things done in Washington.
They'll also have to decide how seriously to engage a progressive movement that sees their assent a historic opportunity to shift the Democratic Party to the left.
"The cavalry is arriving," said Adam Green, cofounder of the Progressive Change Campaign Committee. "A lot of news coverage after the election focused on Democrats winning two seats, but the big story for us is the composition of the Democratic caucus has moved in a massively progressive direction."
Warren, the consumer advocate who articulates a full-throated populism rarely heard in Washington in recent years, is the most prominent of the new progressive members. But she is far from alone: There's Wisconsin's Tammy Baldwin, who hails from the liberal bastion of Madison; Connecticut's Chris Murphy, a loyal Democrat who replaces the moderate Joe Lieberman; and Hawaii's Mazie Hirono, who during her tenure in the House has been a leading member of the Congressional Progressive Caucus. They are the sort of Democrats who don't mind discussing a strong role for government in American life.
The four incoming senators join progressives Sherrod Brown of Ohio and Sheldon Whitehouse of Rhode Island - both of whom were reelected in November - and other liberal stalwarts in the Senate, among them Bernie Sanders of Vermont, Jeff Merkley of Oregon and Al Franken of Minnesota. Meanwhile, moderates Democrats Ben Nelson of Nebraska, Kent Conrad of North Dakota and Lieberman of Connecticut (an independent who caucuses with Democrats) - all of whom have repeatedly angered progressives - have retired.
The new crop of left-leaning senators and their progressive allies reflect something of a break with the modern Democratic Party. In the 1990s, then-president Bill Clinton and the Democratic Leadership Council successfully moved the party away from the economic populism and leftist positions it had embraced since the late 1960s. It was a vision reflected by Mr. Clinton's decision in 1996 to sign legislation to end "welfare as we know it," and his declaration that the "era of big government is over." Liberals derided the "triangulation" reflected by Mr. Clinton's policies as reflecting an abdication of what the Democratic Party stands for.
Despite claims by some on the right that President Obama has a "socialist agenda" - in the words of Mr. Clinton's onetime aide, Dick Morris, who has been credited as the father of triangulation - progressives have lamented that Mr. Obama has largely not sought to return his party to the unapologetic populism of the pre-Clinton era. While they stood by Mr. Obama in the 2012 election cycle, they rallied enthusiastically around Warren, who did not shy away from deeming the economic and political system "rigged" against the middle class. The rhetoric of Warren and the other new Senate progressives has prompted comparisons to progressive heroes like Paul Wellstone and Hubert Humphrey - along with George McGovern, whose trouncing in the 1972 presidential election helped give rise to the Democratic Leadership Council.
Green says the influx of progressive voices in the Senate will "embolden everybody to advance more progressive priorities." And he argues that polling proves that progressive positions, such as protecting entitlement programs, are embraced by most Americans and thus deserving of unapologetic Democratic support. "There's no reason that any Democrat in the caucus should ever get behind cuts to any of these benefits if they care about what's political popular," he said.
Others are more skeptical.