"You have ballpark 60 districts as diverse as Kansas and Staten Island. One bumper-sticker message will be self-defeating," said former congressman Steve Israel of New York, who led Democrats' national House campaign in 2012. The question is whether that path results in Democrats gaining the 23 new seats they need for a majority. The next test will come with Tuesday's primaries in five states: Maine, Nevada, North Dakota, South Carolina and Virginia. A voter peals off an "I Voted" sticker at a polling location in Larkspur, California, earlier this month. Credit:Bloomberg A key measure of Democrats' leanings will come in suburban northern Virginia, where vulnerable Republican Barbara Comstock has a half-dozen Democrats vying to knock her out of Congress in November. The field spans from establishment favourite Jennifer Wexton, a state senator who touts her bipartisan deal-making in Richmond and says the US should move cautiously toward universal health insurance, to political newcomers with calls for a $US15-hour minimum wage and a more immediate move to single-payer, government health insurance.

Israel disputes that the current House slate represents a notable leftward shift nationally, and national party leaders have still angered liberals with some of their recruitment choices. Still, resistance leaders are confident of their influence. "We are seeing grassroots action and organising in a meaningful way," said Maria Urbina, national political director of Indivisible, founded after Trump's 2016 election. "We see the party apparatus coming in behind some of this action on the ground." To be clear, not every surviving candidate is a carbon copy of Bernie Sanders, the 2016 presidential candidate whose insurgent campaign emboldened the left with his calls for universal health insurance, a $15-hour minimum wage and tuition-free college. But the influence of Sanders' inspired base is palpable, as winning nominees have adopted pieces, if not the whole, of an agenda that has become more typical within the party since it lost the House majority eight years ago. At least to date, it's staved off a Democratic version of the 2010 tea party rise, when GOP leaders, even as they marched in lockstep opposition to then- President Barack Obama, watched archconservative outsiders defeat incumbent Republicans and fundamentally reshape the party's identity on Capitol Hill. The Democratic path seems to be more incremental evolution. A key indicator is the Democratic Congressional Campaign Committee's "Red to Blue" program, the party's top candidates for flipping Republican seats. Twenty candidates with that designation have faced primaries already; only one of them - among the party's most conservative choices - has lost. (About two dozen more Red to Blue candidates have upcoming primaries, and the DCCC could add to its list.)

On health care, at least two of the Red to Blue hopefuls past their primaries call explicitly for single-payer health insurance, four more want a government- run public option, and several others generically call for expanded coverage under the Democrats' 2010 health insurance overhaul. Eighteen were endorsed by End Citizens United, signifying their pledges to block corporations and wealthy individuals from spending unlimited amounts on campaigns. A leftward shift on health care is clear in Arkansas, where state Representative Clarke Tucker dominated a primary as the more centrist choice - he's among the Democrats saying he wouldn't back California's Nancy Pelosi for speaker - in a congressional district Trump won by almost 21 points. A cancer survivor, Tucker does not support single-payer, but he does say all Americans, regardless of age, should be able to buy Medicare coverage. That's quite a leap from 2010, when then-Senator Blanche Lincoln, a self-declared Arkansas centrist, joined other moderate Democrats to back the Affordable Care Act only after a public option was scrapped. She lost her 2010 re-election bid in a landslide anyway. Beyond national Democrats' favored candidates, environmental lawyer Mike Levin won a November ballot spot in a Southern California district championing single-payer. He beat three other candidates who support Medicare-for-all health insurance. Together, the four Democrats received more votes than the eight- member Republican primary field in a district that retiring Rep. Darrell Issa has represented since 2001. "I know that with a bold progressive agenda and with the continued mobilisation of the progressive base in California 49, we're going to win come November," Levin said.

In some instances, the liberal arguments come from candidates who can sell themselves as trustworthy messengers, even if the message is stereotyped as out of place. So Abby Finkenauer in an expansive northeast Iowa district and Colin Allred in metro Dallas can forcefully advocate for ideas like paid family leave, long a goal of the American labour movement. Finkenauer plays up her working-class roots as she also stakes out liberal positions on abortion rights. Allred still looks every bit the NFL defender he was before becoming a civil rights attorney. He's outspoken about LGBTQ rights while endorsing a $US15 minimum wage and a partial semi-automatic gun ban - all notable contrasts with the Republican congressman, Pete Sessions, he's trying to defeat in November. Republicans, meanwhile, say bring it on. "Wacky, far-left positions," said Courtney Alexander of the Congressional Leadership Fund, a GOP super PAC aligned with Speaker Paul Ryan, "aren't going to fly in suburban swing districts this fall." AP