Even before the horrible events in Charlottesville, Virginia, over the weekend, President Donald Trump was having a bad August.

He had already single-handedly escalated tensions with North Korea to the point that a nuclear strike suddenly seemed like a possibility for the first time in many Americans’ lifetimes.

His legislative agenda on Capitol Hill had stalled.

The White House departure lounge was starting to look like a clown car.

And the president’s 34 percent approval rating was the lowest for a new president in the summer of his first term, since Gallup began polling presidential popularity.

Add to that the president’s increasingly waffling response to the terrorism in Charlottesville on Saturday and it’s easy to see why Democrats see an opening — a big one — to exploit in the 2018 midterms.

But how the Democrats move forward toward 2018 is an open question and it’s clear that even Democrats don’t agree on the best way to do that. Should they go hard left to take advantage of the energy in their progressive base? Or try to capture the independents that are up for grabs? Should they do both at the same time?

It’s not unlike the dilemma that Republicans faced themselves in 2010 when President Barack Obama’s approval rating fell to a personal low and the grass roots on the right began to boil over with calls for wholesale change in Washington.

Pushing the impossible

Republicans, at the time, did what they needed to do to win back the House, the Senate, and eventually, the White House. But along the way, they also made a number of promises that would be impossible for them to keep in the real world of governing. Their biggest promise — to repeal and replace Obamacare — was also the root of their biggest failure so far now that they have unified control of government.

I tried to remember at several points this year, as “repeal and replace” started and stopped, where exactly the idea came from? Who in the world promised to dismantle legislation that affected one-sixth of the economy and then to immediately replace it with something demonstrably better in a policy area such as health care that the GOP has mostly steered clear of for decades?

Two of the first people to push repeal and replace were former Sen. Jim DeMint and former Rep. Michele Bachmann. They were both long gone from Congress by 2017 when Speaker Paul Ryan and Majority Leader Mitch McConnell had to round up the votes to really do it.

But if McConnell is looking for someone who is still in Congress to blame for promising voters the impossible — he’ll have to look in the mirror. It was McConnell in 2010, three months after Obamacare passed, who told CNN’s John King that “repeal and replace will be the slogan” for Republican candidates heading into the 2010 midterm elections.

Repeal and replace was the slogan and it worked brilliantly. And why not? Repeal and replace was simple. It was catchy. It reduced a complex problem to a three-word solution and it was so widely embraced by Republicans, from the grass roots to the top leadership, that you couldn’t fault voters for believing that Republicans would not only be willing to vote to repeal and replace Obamacare, they would actually be prepared with comprehensive legislation to do it once they won. None of that turned out to be the case.

Democrats, beware

The GOP’s failure to pass that or any major legislation so far has Democrats confident about their chances next year. But they may be in danger of making the exact same mistake with single-payer health care or “Medicare for All,” an idea that has been around for decades but is suddenly getting new life as a potential litmus test for Democratic candidates heading into 2018.

Like repeal and replace, Medicare for All is catchy. It’s simple. It makes the incredibly complex problem of providing universal health insurance sound easy — Medicare for all! Like repeal and replace on the right, single-payer health care is also popular with the Democratic base and quickly getting more popular with time. A June Pew survey showed that 64 percent of liberal Democrats supported a single-payer health insurance system, which was up 13 points just since January.

But the fine print on Medicare for All is much more complex. For one thing, there is almost no fine print on congressional proposals to extend Medicare to the entire population, which has been introduced repeatedly since the 1990s but remains more of an outline of a proposal than detailed legislation.

The bill from Rep. John Conyers Jr., D-Mich., H.R. 676, broadly expands Medicare to the U.S. population, including currently Medicaid, Medicare and CHIP recipients; bans for-profit insurance companies from participating (with a few exceptions); and pays for it all by increasing certain payroll taxes, introducing taxes on investment income and financial transactions, and raising taxes on the top 5 percent of income earners.

Having a simple, elegant solution to national health care is enticing. But if Democrats win the House and Senate in 2018 and the White House in 2020, are they really promising to dissolve the private insurance industry? What about for-profit hospitals? Would they even have the votes to pass such a bill if they win the White House and majorities in Congress? Those are the details Democrats are promising when they promise to enact “Medicare for All.”

Cost is another detail that Democrats should consider before they turn the concept into a litmus test. Vermont Sen. Bernie Sanders’ presidential campaign estimated that his proposal would need an extra $1.38 trillion in federal funding every year to become reality.

A similar proposal now circulating in California is estimated to cost the state $400 billion annually, which would translate to trillions of dollars in tax increases over the next decade. That may be a value proposition that Californians support, but it’s also the complex piece of the proposal that rarely makes it into the 30-second pitch from Democratic candidates on the campaign trail. A legislative analysis of the bill also warns that it would result in “unprecedented change” and “tremendous uncertainty” in the health care industry in the state.

Before Democratic leaders embrace sweeping legislative promises heading into 2018, they should study the Republicans’ path to this moment carefully. It’s not a place any of them want to be.