(CNN) Democrats return to Washington this week for a new round of combat with Republicans desperate to deliver on their imperiled agenda.

After a long spring and summer at the barricades, pushing back against President Donald Trump's attempts to bulldoze the legacy of his predecessor, the stakes are set. And with 2018 expected to be dominated by heated midterm congressional races, the coming months could be Trump's last best chance to revive his reeling presidency.

"This fall, the insanity of the Trump era is likely to kick up a notch," MoveOn.org Washington Director Ben Wikler said. "It's hard to believe that's possible, but it seems almost inevitable."

Here are five questions staring down Democrats as Congress gets back to work.

1. Can they use the blueprint from the Obamacare fight to defeat other Trump agenda items?

They're certainly going to try.

First up is the Deferred Action for Childhood Arrivals program, an Obama-era policy that protects undocumented immigrants who came to the US as children. With Trump now planning to phase it out , Democrats will lean on their Republican colleagues -- with the aid of a furious grass-roots movement that has been mobilizing for this moment -- to pass legislation, perhaps some form of the DREAM Act, protecting an estimated 800,000 people suddenly at risk.

Democrats will have more say on "tax reform," which figures to be front and center as 2017's legislative clock ticks down. Trump has already begun his push. In between visits to flood-ravaged Texas last week, he formally launched the initiative with a speech in Missouri . Though particulars are hard to come by, Democrats, with Trump's campaign pledges in mind, were quick off the blocks in denouncing it.

Democratic National Committee Chairman Tom Perez warned that any Republican plan would "overwhelmingly benefit the super rich and corporations over hardworking Americans." It's a simple argument and one the party seems poised to rally behind.

"The message war is going to be: Who actually gets the money?" Wikler said. "Trump makes this simple because he is a billionaire, his Cabinet is full of billionaires. People get who he's looking out for."

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Health care, though, is a much more visceral issue, and social welfare programs are famously difficult to roll back. Tax cuts are an easier sell. Democratic lawmakers kept a firm line in the health care fight. But with tough 2018 races ahead, especially for endangered Senate Democrats (more on them soon), defections are a concern.

The plan, as Wikler explains it, is to connect the dots -- back to health care.

"The way we see it is that this spring, Republicans tried to take away people's health care to pay for a massive tax cut for the wealthy. And they failed. Now they're trying to, one step at a time, start with a massive tax cut for the wealthy, and then take away our health care," he said.

As weird and unpredictable as the Trump era has been, and figures to be going forward, an argument over taxes would inject some familiar elements -- and old tropes -- back into the political fray.

"Like with health care, (the 'tax reform' debate) provides Democrats plenty of opportunities to go on the offensive," Democratic strategist Lis Smith said. "Democrats can reclaim the mantle of being the party that fights for people and define Republicans as the party of Wall Street, big corporations and the very, very rich."

Republicans have a lot to lose, too. Defeat for Trump on the tax front could set off a round of damaging defections, both in terms of political backing in Congress and in the halls of the White House, where high-ranking officials like Gary Cohn, his top economic adviser, could flee if another top priority fails.

2. Can Democrats sell their own message -- and not get boxed in by Trump?

Everybody has a plan until the President starts tweeting. But Smith thinks Democrats are developing tougher chins.

"Democrats (in 2016 and early 2017) fell into the trap of just responding to Trump and being in a never-ending outrage loop," she said. "But with every week and month that's passed, they have been getting smarter about not falling into the that trap."

If organizers have a clear idea of how they'll oppose the Republican tax plan, the party is still searching for a bold-faced message to compete with Trump's amorphous but evocative promise to "make American great again." This summer, they trotted out the "Better Deal" platform , signaling a renewed focus on economic issues. Inside the Beltway and in activist circles, the policy prescriptions were greeted optimistically. But Trump's grip on the national political narrative was never in doubt.

So how do Democrats break through?

Nick Rathod, executive director of the State Innovation Exchange and an Obama White House veteran, pointed to the "Fight for $15," a union-backed grass-roots push to raise the minimum wage, as an example of how the party can pick up steam despite its deficit in Washington.

"Congress is in perpetual gridlock, Trump is doing whatever, and while I don't recommend taking your eye off the ball federally, where you can actually make change and actually make a difference is at the local level," he said. "That's where I think people should be organizing and working."

The Service Employees International Union and the "Fight for $15," which it helped launch, tapped Sanders to be the face of a new campaign, begun on Labor Day, to push back against Republican efforts to gut organized labor in the Midwest and Rust Belt.

"There are only two ways for workers to win higher pay," Sanders said in a video touting the effort, which will chip away at anti-labor elected officials ahead of the 2018 midterms. "No. 1, we've got to increase the minimum wage. And second of all, we have got to build strong trade unions."

Sanders is a potent political weapon, one that the party writ large has become increasingly comfortable with as one of its most prominent public spokesmen. Shut out of the nitty-gritty of trying to legislate on Capitol Hill, Rathod argued that Democrats should take a cue from Sanders and quit living in fear of pushback from conservatives.

"Democrats should stop second-guessing themselves so much and really put forward a broad vision that's bold and pushes the envelope and see what happens," he said. "It's OK for people to poke holes in policy, it's always going to happen. But leading with our values -- big and bold -- is what leadership is about. People will follow that."

3. Can Democrats on Capitol Hill stick together and vote as a group, even under siege by the White House?

Trump is attempting to make this hard -- particularly on tax reform.

The President traveled to Missouri on Wednesday, where he told voters to oust Democratic Sen. Claire McCaskill if she votes against his tax package.

This week, Trump is set to visit North Dakota, the home of Sen. Heidi Heitkamp -- like McCaskill, a Democrat up for re-election in 2018 in a state Trump easily won in the 2016 election.

An administration official said the President has committed to a once-a-week travel schedule that would allow him to leverage his lasting popularity among Republicans to target other vulnerable Democrats.

It's a much more organized strategy, and a more direct role, than the White House used during the health care fight, during which Trump didn't hit the road to pressure Democrats to break ranks.

Democrats stuck together through the legislative battle over health care. They didn't have a vote to spare, either. But tax-and-spend issues could present more of a challenge, particularly if Republicans bundle several items together in a single package.

The three to watch: Heitkamp, Indiana Sen. Joe Donnelly and West Virginia Sen. Joe Manchin. They were the three who didn't sign a letter laying out Democratic tax reform priorities earlier this year -- and therefore are Trump's ripest targets.

4. Can the party keep the grass roots engaged?

Serafina Ha of Chicago and Disciples of Christ Refugee and Immigration Ministries Director Sharon Stanley-Rea lead chants during a demonstration in favor of immigration reform in front of the White House (Chip Somodevilla/Getty Images)

The fight to spare Obamacare from the congressional GOP's repeal effort gave the Democratic base a rallying cry and a unifying goal -- allowing older parts of the party's establishment, new organizations like "Indivisible" and leftist groups like the Democratic Socialists of America to line up behind a common cause

The next big clash for the coalition is expected to come over the future of DACA recipients, as the administration threatens to end DACA by March of next year. That could run into the battle over border wall funding, leading to tense December negotiations.

But with a shock victory on health care under their belt, don't expect progressive activists to settle for anything less than continued, all-out opposition to the White House.

The dangers of straying from that strategy were evident when Sen. Dianne Feinstein (D-California), in San Francisco last week, said of Trump: "I just hope he has the ability to learn and to change, and if he does, he can be a good president. And that's my hope."

The comment drew swift condemnation from some in Feinstein's home state.

"We don't have much patience for Donald Trump here in California," said California state Senate Democratic Leader Kevin de León. "This President has not shown any capacity to learn and has proven he is not fit for office. It is the responsibility of Congress to hold him accountable -- especially Democrats -- not be complicit in his reckless behavior."

The episode showed the swiftness with which progressives will punish any Democratic lawmakers responsible for cracks in the wall of opposition to Trump -- and how critical maintaining that wall is to channeling the grass roots.

Which bring us to ...

5. Can the Berniecrats and party establishment stick together and iron out a winning agenda?

There are two ways to look at the ongoing, sometimes tedious, always heated debate over the future of the Democratic Party.

One viewpoint holds that the divisions are overblown and that Democrats -- actual voters -- are for the most part pretty closely aligned on policy questions. Many who proudly cast ballots for Clinton last November would happily vote for Sanders in 2020.

And then there is the other, more dire version of events. In this world, Berniecrats are at war with the Democratic establishment for the soul of the party. Sanders represents a progressive push to take power for the working class, while the moderate or centrist wing zealously defends neo-liberal policies (like an embrace of "market-based solutions" in place of public programs) that enrich the elite and fuel growing economic inequality.

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There is a bit of truth in both. The party is at once coming together -- especially on Capitol Hill -- and tearing itself apart, usually over social media, as competing ideologies jockey to keep or seize power in the aftermath of Trump's win and a decade of Democratic losses in the states.

Luckily for the Democrats, Sanders is more deft and pragmatic than many suppose. Even as he openly condemns the party's missteps, the Vermont senator is growing his slate of allies in the Senate. His national popularity helps -- the courtship process has, so far, mostly bent in his favor. Support for single-payer health care, or "Medicare for all," dismissed by Clinton in January 2016 as an "idea that will never, ever come to pass," is a good enough bet to be written into the party's next platform in 2020.

Sanders plans to introduce his new version of the bill in mid-September, this time with support from some of the party's most popular and ambitious figures. California Sen. Kamala Harris, like Sanders, an early favorite to run for the nomination in three years, announced last week that she would co-sponsor the legislation, which, though dead on arrival in a Republican Congress, has quickly emerged as litmus test for Democrats seeking higher office.

Claire Sandberg, a progressive activist and former digital organizing director for Sanders during his primary bid, said the lesson here is simple: "Organizing works."

"Centrist Democrats are starting to come around on 'Medicare for all' because they've been the recipients of sustained pressure from their constituents," she said. "This shift is a positive development but also a reminder that it will take exponentially more organizing to actually win."

For now, though, after more than a year of internecine brawling, even modest signs of détente -- and an emerging consensus -- are something for Democrats to celebrate. Whether it can help vault them back into power is another question.