That referendum will be won or lost in swing districts—and they are much harder to find than they used to be. The Cook Political Report found that the number of swing seats—where neither party runs more than 5 points better than it does nationally—has dropped by more than half over the last 20 years, from 164 to 72. The most vulnerable seats in the current House majority belong to 23 Republican incumbents in districts Hillary Clinton carried, largely clustered in the suburbs of major metropolitan areas like Los Angeles, Philadelphia, and Washington. These districts tend to be mainstream in tone and interest. That’s a tough place to win the hand Trump has dealt Republicans of cutting student aid, denying climate change, and eliminating protections for pre-existing conditions.

But Democrats don’t just need to choose the right battles, they also need to choose credible candidates who can win them. Candidate quality may not make the difference in a place like Montana’s at-large district, where Greg Gianforte won handily just hours after assaulting a reporter. Winning hotly contested swing seats, however, requires candidates who closely match their districts—even if they don’t perfectly align with the national party’s activist base. In 2006, the Democratic base was energized and angry, but then as now, capturing a majority required winning some tough races in red and purple states across the heartland. As leaders in that 2006 effort, we recruited a football player in North Carolina, a businessman in Florida, an Iraq veteran in Pennsylvania, and a sheriff in Indiana. The Democratic Party won twice as many seats as it needed to gain control.

There’s a long-term payoff for a party that gets this right. Good candidates not only help build a wave, they help sustain it. Wave elections offer the chance to establish new beachheads in hostile territory, but it takes gifted leaders to survive when the pendulum swings back. In the 1980 Reagan landslide, Republicans gained 34 House seats—only to lose 26 seats two years later—and 12 Senate seats, only to lose 8 senators and Senate control when those seats came open six years later. With the right candidates, the impact of a wave can be felt for decades. Half a dozen “Watergate babies” elected to the House in 1974 went on to serve in the Senate. So have three Democrats who joined the House in the 2006 wave.

Even with the right candidates in the right districts, a wave won’t get far without a credible plan to address the country’s problems, not simply run attack ads against the parade of horribles from the other side. In 2006, we published a book called The Plan, which offered detailed proposals on college, retirement, health care, and the economy. One reason today’s congressional Republicans are struggling to enact an agenda is that unlike the Contract-with-America Republicans of 1994, the GOP waves of 2010 and 2014 were built only on saying no to Obama.

Donald Trump may hand Democrats the election next year, but Democrats should strive to earn the people’s trust on their own merits anyway. These are serious times for a country at the mercy of an unserious president. The damage may take years to repair, and voters deserve to know what Democrats are going to do about it.

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Bruce Reed is the former chief of staff to Vice President Joe Biden, and the former CEO of the Democratic Leadership Council.