This is the moment for the Democrats. Can they seize it or will they let it slip away?

With President Trump entangled in scandals, his approval ratings at historic lows, and a growing number of disaffected Republicans voicing their opposition, the Democratic Party has a golden opportunity to embrace the disgruntled majority of Americans desperately seeking alternatives.

Yet, there remain bitter divisions within the party. You might never know the primaries ended 18 months ago. Hillary Clinton continues to blame Bernie Sanders for her loss to Trump, and Sanders has repeatedly stated that the party needs a more progressive message.

Internal rifts have only grown over how to address the challenges and opportunities presented by President Trump. Should Democratic candidates move to the left or to the center? Is it more effective to court white working-class voters who have traditionally voted Democratic, but bolted for Trump in 2016? Or should the party double down on the Obama coalition of minorities, millennials, and the professional class?

This will be the political frame as we enter the midterm elections, Donald Trump reshapes the Republican Party in his own image and remains intolerant of competing Republican views, and Democratic leaders begin to emerge and prepare for the next presidential election.

About the only consensus among Democratic leaders is that the party must expand its base and ensure that different voices are heard. It’s not rocket science: a party with a broader and more ideologically diverse base will do better in elections than a party that appeals to a narrow constituency.

Internal efforts to divide the Democratic party do little to brighten 2018 prospects and much to ensure long-term damage to party unity. Litmus tests, such as demanding that all Democratic candidates unequivocally embrace single payer healthcare, are counterproductive. Such a purity test needlessly impedes efforts to fix our healthcare system, and makes it difficult  to attack Republicans for supporting a bill that the Congressional Budget Office had predicted would strip millions of coverage and raise premiums on the most vulnerable. The recent proposal of a Medicare For All bill opens the door for Republicans to divert attention from their disastrous attempts to repeal the Affordable Care Act, and to criticize Democrats for supporting socialized medicine. All this effort for a bill that in a Republican controlled Congress has no chance of becoming law makes little political sense.

Another corrosive litmus test has been proposed by billionaire Democratic donor Tom Steyer. He has pledged to only support candidates who vow to impeach President Trump. While Trump’s twitter tantrums, disregard for facts, potential violation of the Emoluments Clause, and possible collusion with Russia should disqualify a commander in chief, such a purity test is imprudent. Progressives clamoring for impeachment should let Special Counsel Robert Mueller’s investigation run its course. Such unequivocal demands that the president be impeached are not only unrealistic given the current political climate, but also have the chance to backfire. In 1998, House Republicans campaigned on impeaching President Clinton and ended up handing back control of the chamber to Democrats, the first time in 176 years that the party of the president gained seats in a second term. In 2018, Democratic Senators are running for reelection in ten states that Trump won. Given that Democrats need to win 24 House seats for a majority, taking such absolute and polarizing positions is politically risky.

Attempts to associate Never Trump Republicans with Trump are also unhelpful, and those Republicans should be courted rather than discredited.

After Senator Jeff Flake passionately denounced President Trump on the Senate floor last month and called for civility and compassion, he validated Democrats’ claims against Trump. Yet DNC chairman Tom Perez decided to blame Flake. Citing Flake’s close voting record with Trump, Perez wrote in a statement, “[Flake’s] retirement is symbol of a Republican Party whose leaders allow Donald Trump’s divisive politics to flourish as long as it serves their political interests, and who fail to criticize this dangerous president until it’s too late.” Such criticism of fervent opponents of Trump risks alienating voters in the center. If Democrats want to succeed in 2018 and beyond, they should aim to win over middle-of-the road voters who have been alienated by the president and Republican leadership.

How can the party succeed in next year’s midterm elections? A first step would be understanding the need to expand the base and build a big tent party. In a party with an angry and increasingly activist base, there is certainly a role for progressive icons such as Bernie Sanders and Elizabeth Warren. Yet alienating moderate voters by imposing litmus tests or attacking those who are deemed insufficiently progressive is a recipe for failure.

If Democrats want to retake control of the House next year, they should look to the 2006 playbook of DNC Chairman Howard Dean. Dean shrewdly led a 50-state strategy, designed to make Democrats successful in conservative-leaning districts. To accomplish this, the party sought to run candidates that fit their districts, aware that, for instance, a coastal liberal would not win in a southern conservative district. As Rahm Emanuel, then leader of the Democratic Congressional Campaign Committee, wrote, “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.”

A bold and progressive policy agenda can excite base voters and pave the way for success in midterm elections, where turnout is historically lower. But a highly motivated base will not be enough to win swing districts. Recent successful Democratic presidential candidates, such as Bill Clinton and Barack Obama, knew that they had to build center-left coalitions and focus on economic growth, fiscal responsibility, and preserving social safety net programs. Democrats should certainly continue to draw a stark contrast with Trump. But 100 percent purity tests will only hinder the party’s ability to win over crucial swing voters, preventing the party from ultimately prevailing.