At the grass-roots level, there’s reason for the left to be optimistic. While there’s not yet enough data available to draw finer conclusions about the left-wing resistance, Skocpol called the scale of the women’s marches around the country “pretty remarkable.” But she tempered this with caution. “What I don’t know is how much sustained organizing is going on in states and districts across the country.” The most active tea party groups Skocpol encountered held monthly meetings, invited speakers and formed committees to stay informed on what was happening in their state legislatures. “I know that the Indivisible site lists thousands of groups, but I don’t think we know how persistent they are,” she said.

The left also faces challenges related to the demography of its traditional constituencies – younger, more diverse — that tend to vote less than the older, white base of the Republican Party, particularly in special elections and midterms. Where the left’s movement could go wrong, Skocpol said, was being too fixated on demonstrations. “It’s got to transfer to votes.” Using the base’s energy to register left-leaning voters and turn them out to the polls will be the ultimate test of grassroots success.

On a larger organizing scale, the tea party’s affiliation with professional advocacy groups helped amplify their cause and at times helped find money for candidates that lived up to the group’s ideals; Scott Brown’s special election to the U.S. Senate in 2010, taking Ted Kennedy’s seat, was funded in part by a tea party PAC. Where the left could stumble — particularly the far left — is with a lack of cooperation with big-money donors and organizations. “Groups such as FreedomWorks were absolutely vital,” former tea party organizer Ben Howe wrote in an email. “People have short attention spans and are fickle with their motivation levels. Having a funded group whose entire job is to organize events for voters to attend kept the ball moving at all times.