Rep. Donna Edwards. (J. Scott Applewhite/AP)

Republican leaders have spent recent elections agonizing over divisive primaries pitting conservative activists against the GOP establishment. Now, Democrats are increasingly the ones grappling with a restive base.

In municipal and statewide Democratic primaries all across the country, liberal candidates have emerged in strong competition against more moderate opponents at a time when the party base is increasingly longing for populist, outspoken standard-bearers. The result could be something akin to what Republicans have dealt with as tea party candidates have been battling centrist Republicans.

The rise of liberal contenders comes as activists have launched a movement to draft Sen. Elizabeth Warren (D-Mass.) into the presidential race, but she has shown no signs that she is planning to jump in. That has left many wondering whether issues like income inequality will be sufficiently addressed in 2016 by presumed early Democratic front-runner Hillary Clinton.

But there is less doubt about those issues surfacing in smaller-scale races. The latest contest where a liberal contender has become a factor is the Maryland Senate race, where Rep. Donna F. Edwards (D) announced her campaign Tuesday.

Her main competition is Rep. Chris Van Hollen (D). As Mike DeBonis noted Monday, Edwards, one of the seven most liberal members of the House according to National Journal, can stake out ground to the left of Van Hollen on fiscal matters like across-the-board budget cuts known as sequestration that she opposed but he supported. Edwards voted against the budget deal that resulted in the cuts while Van Hollen voted for it.

But Van Hollen vigorously opposed the cuts, and offered an alternative to them. If the issue surfaces in the campaign, Van Hollen can point to that opposition in defense of his record.

In Chicago, liberal upstart Jesus "Chuy" Garcia has given Mayor Rahm Emanuel a stronger-than-expected challenge. He has run a campaign casting Emanuel as a mayor who has catered to the wealthy at the expense of everyone else in the city, hammering the incumbent on crime, education and economic issues.

Last month, one national liberal group asked its members whether they would like to see Sen. Ron Wyden (D-Ore.) get a primary challenger over his position in support of expanding President Obama's trade authority, an idea that has been panned by many on the left as a job killer.

In some races, liberal candidates have cleared or are expected to clear the field, signs that even though the 2016 presidential race may not be shaping up as a dream scenario for liberal activists, down the ballot, there are plenty of reasons for them to get excited.

California Attorney General Kamala Harris (D) is clearing the field in the race to succeed retiring Sen. Barbara Boxer (D). Harris, who was endorsed by Warren and has waged legal fights against big banks, is the clear early front-runner. Other top potential candidates like billionaire climate activist Tom Steyer and former Los Angeles mayor Antonio Villaraigosa declined to compete against her.

In Wisconsin, former senator Russell Feingold (D) appears to be moving closer to a rematch against Sen. Ron Johnson (R). Feingold, who has loyal liberal following, is viewed by Democrats across the ideological spectrum as the strongest possible challenger against Johnson.

Many of the Democrats who liberal activists want to defeat — Van Hollen and Emanuel, for example — have addressed concerns that they are not liberal enough head-on. They have highlighted their efforts to fight for middle-class people. The primaries are not neatly divided on every issue, making for a potentially contentious nominating process.

A key question for Democrats is what the 2016 primaries will mean for party unity. It can be a double-edged sword, as Republicans have shown.

The rise of the tea party in 2010 energized many conservative voters to come out and vote in a wave election that swept Democrats out of power in the House. But it also gave rise to a series of nasty, expensive primaries that many Republicans feel cost them winnable Senate seats like Colorado's in 2010 and Indiana's in 2012.

The tea party's rise has also made governing more difficult for the GOP congressional majority as rogue conservative members continue to demand a fight against Obama's agenda, even if it leads to things like a partial government shutdown.

Open presidential primaries are typically the arena for deciding the future direction of the party. For Republicans, there seems to be a prospective 2016 White House hopeful for just about every part of the ideological spectrum. And many of them stand a real chance of winning the nomination.

But Democrats don't have nearly as many feasible options. In the minds of many in the party, the conversation begins and ends with Clinton, who, as shown by the draft-Warren movement, is not a choice that will fully satisfy the left.