After a string of disappointing midterm and general elections during the Obama era, the Democratic Party was rendered largely inert and anemic, saddled with minorities in both Houses of Congress. But now, the calculus has changed. House leadership forced Donald Trump into an unenviable corner when it introduced its flawed, unpopular Affordable Care Act alternative last week. If the president is unable to steward a “repeal and replace” bill through the House and the Senate—a promise that, in part, carried him all the way to the White House—his administration will suffer an almost insurmountable setback that would impede G.O.P. momentum on Capitol Hill, delaying crucial agenda items and campaign pledges such as tax reform, deregulation and infrastructure—most notably, Trump’s southern border wall. Democrats smell blood. So as Trump dispatches milquetoast tweets, asserting that Republicans are making progress on health-care, his rivals from across the aisle are preparing to pillory him and the G.O.P. over the measure in 2018.

“We are on offense and united. They are on defense and divided, the opposite of what people would have predicted a month or two ago,” Senator Chuck Schumer said in an interview with Politico published Sunday. With public support for President Barack Obama’s signature health-care legislation at an all-time high, Schumer and the rest of the Democrats intend to capitalize on the inevitable fallout from an Obamacare repeal, which they hope to ride to a majority in the House and gains in the Senate. “It was easy [for Republicans] to be critical of Obamacare when you thought it would stay in place. Now that the chance of repeal is real, people are much more worried,” Schumer added. Tim Kaine echoed the sentiment. “The threat was always very theoretical. Now it’s very real,” the Virginia senator, who is up for re-election next year, said to Politico. “I have colleagues where Hillary and I lost but they won [in 2012] where it was really tough. But the repeal of the ACA is one of the things that’s working in their favor right now.”

In many ways, the Democratic Party in 2017 mirrors the G.O.P. in the early years of Obama’s presidency. Without a leader, Democrats are figuring out how to deal with the increasingly vociferous—and popular—progressive wing of the party, led by Senators Bernie Sanders and Elizabeth Warren—which, to an extent, resembles the Tea Party movement. And just as Republicans transcended their intra-party discord by uniting against Obamacare, Democrats are zeroing in on G.O.P. efforts to dismantle the controversial health-care law. “People now have a greater understanding of what’s at risk of being lost,” Rep. Joe Crowley, chairman of the House Democratic Caucus, said to Politico, adding that Republicans will soon experience the Pottery Barn rule of governing—that if they repeal the law, “they own it.”

Democrats are betting on health-care being as politically toxic to the G.O.P. as it has been for them over the past seven years. “Public sentiment is against blowing up the Affordable Care Act,” Chris Van Hollen, the chairman of the Democratic Senatorial Campaign Committee, told Politico, before adding, “That’s going to become clearer and clearer.” Jettisoning the “Make America Sick Again” slogan, Schumer and his Democratic peers in the Senate have already branded the House bill introduced last week as “Trumpcare”—a harbinger of the messaging strategy the Democrats plan to employ in 2018. Or as Rep. John Larson of Connecticut laid it out to Politico: “If you want a check on Donald Trump, just look at what’s happening with the Affordable Care Act and elect Democrats.”

Trump, for his part, is preemptively blaming the Democrats for the brewing health-care nightmare. On Friday, the president asserted that 2017 is “the year [the Affordable Care Act] was meant to explode because Obama won’t be here”—a claim he doubled down on on Saturday. “We are making great progress with healthcare. ObamaCare is imploding and will only get worse. Republicans coming together to get job done,” the president wrote on Twitter.