OPINION — By shutting down the government, Donald Trump unintentionally gave Democrats the biggest gift possible: Unity.

It could doom his presidency. Stunningly, it is a repeat of the exact mistake he made by choosing Obamacare repeal as his first legislative fight.

In the immediate aftermath of the 2016 election, a dozen shellshocked progressive groups gathered to predict where the national debate would go — and how we could prepare.

The answer was obvious: Donald Trump would push immediately for an infrastructure package.

It wouldn’t be a good package. It would likely entail selling off public roads and bridges to Wall Street and foreign investors. It would mostly be corporate tax giveaways and create very few jobs.

But we feared it could potentially seal Trump’s re-election. Some congressional Democrats would settle for crumbs — agreeing quickly to marginal benefit for their districts instead of holding out for something much bigger, impactful and popular.

With the stock market and job growth organically improving after President Obama’s presidency, Trump passing even a placebo “jobs package” would allow him to take credit. And this first fight could set a precedent of Democrats dividing amongst themselves, paving the way for more Trump policy victories.

Then came the giant unforced error. Trump’s push of Obamacare repeal achieved the remarkable task of unifying all Democrats from Joe Manchin and Elizabeth Warren in the Senate to corporate-aligned New Democrat leader Jim Himes and Progressive Caucus leader Pramila Jayapal in the House. Trump set a precedent by emboldening Democrats to unify against him in future fights.

He just did it again.

As the new Democratic House began, Democrats were ripe for division. Nancy Pelosi’s leadership was under siege in her own party, fracturing the Democratic Caucus.

Meanwhile, there were clear divisions among incoming House freshmen. Those who flipped districts “Red to Blue” were starting to organize as their own bloc. Those who advocated Medicare for All in their competitive primaries before winning competitive general elections — such as Katie Hill of California, Haley Stevens of Michigan, and Sharice Davids of Kansas — were at risk of being isolated from Alexandria Ocasio-Cortez, Ayanna Pressley, and others who flipped blue districts to more vibrant progressive representation.

But as the Cook Reports’s Amy Walters pointed out on Twitter, “The fight over the wall and shutdown has done more to unify Dems that it has to ‘rally’ the Trump base.”

Democrats who wanted to stab Pelosi in the back are now watching her outmaneuver Trump and get national praise for it — creating no incentive other than to root her on.

Instead of being isolated, Ocasio-Cortez was seen leading many “Red to Blue” House freshman through the hallways of the Senate to tell Republican Leader Mitch McConnell to reopen the government. They knew that walking alongside her, and her millions of social media followers, was the best way to amplify their own message. And along the way, they built camaraderie and trust.

A similar collaborative letter to McConnell was signed by blue-district progressive powerhouses Rashida Tlaib of Michigan and Ilhan Omar of Minnesota; self-perceived moderates Mikie Sherrill of New Jersey and Abigail Spanberger of Virginia; and those like Stevens, Hill and Davids, who campaigned progressively but were at risk of being isolated from the blue-district rockstars.

Hill even went on Chris Hayes’ progressive-leaning MSNBC show to announce a big “Shut down the wall, open the government” day of action in conjunction with MoveOn and other progressive groups on Jan. 29 — the day originally slated for Trump’s State Of The Union. 

This partnership among House freshmen facing a common enemy in their first fight will be highly consequential for upcoming legislative debates.

Issues like Medicare for All, a Green New Deal, expanding Social Security, making college debt free, challenging Big Pharma, strengthening voting rights, and combating corporate money in politics are all opportunities to showcase to voters the big, popular ideas Democrats will advance if given more power in 2020.

Not all Democrats will start off on the same page in these debates, and it may take years to push these ideas into law.

But Pelosi and other House leaders will look at whether there is critical mass within the Democratic Caucus when deciding whether to even kick off these debates with hearings, votes and focus. After fighting alongside each other, it is now way more probable that swing-district House freshman will trust their progressive colleagues and give critical mass to bills they may have been on the fence about supporting otherwise.

And impeachment? If any House freshmen were under the illusion that Trump was a rational actor they could deal with — if only there were more rhetoric about “problem solving” — that illusion is fading. Now that Trump has poisoned the well for side deals, there is little down side to following the facts on his law breaking.

As Donald Trump faces increased accountability and sees 2020 voters inspired by increased congressional consensus for big progressive ideas, he will have himself to thank.

Adam Green is the co-founder of the Progressive Change Campaign Committee.