It’s a catchy, irresistible image for Trump-hating liberals: a “blue wave” washing across the country in this fall’s midterm elections, lifting the Democrats back into congressional power. And maybe the party really will score wins in suddenly competitive districts in reliably red strongholds like Utah and Texas and Nebraska. “Certainly we have a lot of work to do,” says Charlie Kelly, the executive director of the House Majority PAC. “But I feel very confident. The underlying dynamics and the metrics right now, across the map, this is very different than the other cycles I’ve seen.”

As much as the Democrats promote the idea of a national wave, though, the core plan to win a House majority resembles a pair of widely spaced, parallel shorebreaks, running along the East and West Coasts. Or, less poetically: “If we don’t win a bunch of seats in California and New York, we’re fucked,” a Democratic congressional strategist says. “Those are the roads to winning back the House.”

Those roads are paved with numbers. The Democrats need to gain 24 seats to reclaim a House majority. California has the largest number of vulnerable G.O.P. seats: 8 out of the 14 Republican-held districts. New York is right behind, with five out of nine.

But two races in particular illustrate why the current Democratic optimism needs to be tempered with some cold reality. The first is a Democratic must-have, a Southern California district that should be a relatively easy flip from Republican to Democratic. Darrell Issa announced his unexpected retirement after representing the 49th district for nine terms; Issa squeaked by in 2016, winning by just 1,621 votes, and Trump is fairly unpopular even in conservative Orange County and northern San Diego.

“The Virginia governor’s race last fall, where Ralph Northam beat Ed Gillespie, proved that socially progressive voters, properly motivated, outnumber Trump voters,” says Brian Fallon, a national Democratic strategist who was Hillary Clinton’s spokesman in 2016. “And we saw good trends with young voters, with people of color, and with college-educated whites in the suburbs. There are a lot of 2018 House races where the electorate looks like northern Virginia. Places like Orange County in California.”

One side effect of the surge in Democratic enthusiasm, however, is crowded and messy primaries. Doug Applegate, who lost to Issa narrowly two years ago, should be the obvious favorite for the nomination: he’s a 63-year-old retired Marine colonel who backed Bernie Sanders for president. Yet Applegate was accused of stalking and threatening his ex-wife; the allegations, which he has denied, hurt his candidacy against Issa in 2016 and could be crippling in the #MeToo era.

The most interesting contender is Sara Jacobs. Being young (28) and female would seem perfectly tailored to the Democratic electoral moment. Yet two white men—Mike Levin, 39, an environmental lawyer and former county Democratic Party official, and Paul Kerr, 62, a Navy vet-turned-real estate investor—are attracting establishment backing and are probably leading the six-person field. “My campaign is not the type that the old boys’ club really knows how to handle,” Jacobs says. “I’m used to being underestimated.”

Jacobs, who has a trans male sibling and powerful party connections—she’s the granddaughter of Irwin Jacobs, a Qualcomm founder and major donor—worked at the U.N. and was a low-level foreign policy adviser to Hillary Clinton’s presidential run. “I am young, but it’s my generation that’s going to have to fix what Donald Trump is breaking, so we should have a seat at the table now,” she says.