With Democrats on defense across the board in Senate races, their hopes in 2014 could rest heavily on their ability to turn out their base — which is to say, voters who are less likely to go to the polls in midterm elections.

That’s one reason you see Dems placing such a heavy emphasis on economic populism and inequality right now — to gin up minorities and low income women, who could be critical to Dem chances in red states.

One thing that could play a key role in that effort: the Medicaid expansion.

The liberal group CREDO is running an interesting campaign. It is circulating state-level petitions designed to put pressure on GOP governors to opt into the Medicaid expansion. While it remains to be seen if such efforts will bring any pressure at all on Republicans, they are useful in that they suggest the Dem base may be energized on the issue, in states that are important in 2014.

In states with key Senate races, over 6,600 have signed CREDO Mobilize petitions in North Carolina, over 4,300 have signed in Georgia, and over 1,600 in Louisiana. In states with important gubernatorial races, more than 12,000 have signed petitions in Florida, and nearly 10,000 have signed in Texas. And it’s early days.

Jennifer Duffy, who analyzes statewide races for the nonpartisan Cook Political Report, tells me that base turnout will be critical for Dem chances, and that the Medicaid expansion is just the sort of issue that liberals can use to mobilize that base.

“For Democrats in Senate races this cycle, getting their base out is going to make the difference,” Duffy says. “They need every vote from their base they can get if they are going to hold the majority.”

The Medicaid expansion, Duffy adds, is one area where voters can really see tangible stakes, even if Obamacare overall remains unpopular. “People see the benefits — this is a pocketbook issue for them,” Duffy says. “They need to get the base excited about something. This is a silver lining in a tough issue.”

Duffy says that in Senate races in North Carolina and Georgia and Louisiana, a lot turns on turnout levels among “minorities and low income women, waitress moms, single mothers.”

The Medicaid expansion, as an issue, is kind of taking on a life of its own, independent of Big Bad Obamacare. In Louisiana, Senator Mary Landrieu has aggressively criticized the rollout of the law, but has also attacked Republicans for refusing to implement the Medicaid expansion. In Georgia, Dem Senate candidate Michelle Nunn has called for fixes to the law while also saying the state should expand Medicaid, which 57 percent of Georgia voters support, according to a recent poll. Democrats are attacking GOP governors over it, too, particularly in the bid to oust Florida Governor Rick Scott.

Meanwhile, the expansion could hold pitfalls for Republicans, because as enrollment mounts, they may be pressed to say whether they really support taking that coverage away from people. Mitch McConnell was recently asked to comment on Kentuckians benefitting from the law, and he filibustered. The GOP Senate candidate in West Virginia is gung ho for repeal but has hedged on the expansion, and the Dem candidate there supports it. And Jonathan Bernstein surveyed GOP gubernatorial candidates and found they’re surprisingly mute on the issue.

Meanwhile, even as the Dem candidates in difficult races distance themselves to varying degrees from Obamacare, liberals can move separately to mobilize the base around the Medicaid expansion. You will be seeing more of that.