With their repeal effort dead for now, Republicans still need to make some difficult health insurance decisions. The Post's Paige W. Cunningham explains what comes next. (Jenny Starrs/The Washington Post)

Senate Republicans waved the white flag last week on their months-long effort to repeal the Affordable Care Act. But by the looks of his Twitter account, President Trump really wants Congress to keep trying.

There are a few ways Congress could restart its efforts to repeal the ACA, or Obamacare, but most would exact a serious cost on Republicans' agenda, their popularity and the health insurance markets.

But since the president wants to know, here are four ways Obamacare repeal could rise from the dead, ranked from least to most likely.

4. The Trump administration lets parts of Obamacare collapse.

Thus forcing formerly reluctant Republicans back to the negotiating table. Trump could do this two ways, both of which he hinted at in tweets recently:

Let's take these threats one by one.

Trump could stop issuing federal government payments to insurance companies. Insurers rely on these payments to make up for lower-income people, who pay less for health insurance under Obamacare.

But: Most health-policy experts agree that if these subsidies are taken away without a change in how much lower-income people pay for their health insurance, insurance markets would implode, forcing insurance companies to leave Obamacare exchanges, thus causing Obamacare itself to implode.

This option is basically a giant game of chicken with Republicans in Congress, and the health-insurance market is the one that could take the fallout.

Another option is that Trump could stop paying subsidies for members of Congress and most of their staff. Obamacare shifted Congress off its federal government health plan and onto the Obamacare exchanges. It looked politically dense for members of Congress to pass an unpopular law they were exempt from. But lawmakers aren't entirely on their own. Just like employees in the private sector get contributions from their employers to buy health insurance, the federal government pays for portions of members of Congress' health insurance on the exchanges.

But: Getting rid of those subsidies isn't all that unpopular with some Republicans. Some conservatives have pushed bills to end these federal contributions for themselves and their staff. So, this may not be a threat that has much leverage.

After failing to repeal and replace the Affordable Care Act, Republican leaders said it will "implode." Health-care experts disagree, saying the ACA is stable under current law — but President Trump and congressional Republicans could change that. (Daron Taylor/The Washington Post)

3. Republicans push off tax reform.

Republicans had been rushing to pass a health-care bill because they're running up against a legislative deadline to do so and avoid a Democratic filibuster. (To pass an Obamacare repeal with just 51 votes instead of 60, they have to pass it while they're debating the budget.)

This fall, Republicans need to start planning for next year's budget, which is due Oct. 1. They had hoped to use that budget process to pass tax reform — again under a budget rule that lets them duck Democrats' wrath in the Senate. Now, Republicans will have to decide: Do they want to do tax reform, or health care?

“Until health care is off the budget tracks,” said Sarah Binder, a procedural expert at the Brookings Institution, “a tax reconciliation bill is stuck in the rail yard.”

But: There isn't the political will to keep pushing health care. Key conservatives — even huge proponents of getting something, anything, done on health care — now say it's time for Republicans to cut their losses and move on to something else.

“Quarantine it,” said Josh Holmes, a GOP strategist and former chief of staff to Senate Majority Leader McConnell (R-Ky.) who coined the “repeal and replace” mantra in 2010. “You can let it destroy your entire agenda and your entire party as a result of inaction by continuing to dwell on something that, frankly, they’ve proven unable to do.”

2. Senators who were a “no” become a “yes.”

Depending on what plan Republicans would put up, they would need from three to six Republicans to change their minds.

But: For this to work, something drastic would have to change in the legislation. The Senate's repeal/replace bill lost six Republican votes last week, from conservatives and moderates.

Another option: a senator who was a “no” isn't present for voting. Then, the Senate doesn't just need a majority out of 100 senators; they'd need a majority out of 99, writes Stan Collender, a budget policy expert with Forbes.

Sen. John McCain (R-Ariz.) is back home in Arizona in treatment for a particularly brutal type of brain cancer. His office says he “plans to return to Washington at the conclusion of the August recess.”

1. Republicans start working with Democrats to make tweaks to Obamacare.

Senate Minority Leader Charles Schumer (D-N.Y.) spoke about the failure to pass the Republican's "skinny repeal" bill, commending Sen. John McCain (R-Ariz.), Sen. Susan Collins (R-Maine), and Sen. Lisa Murkowski (R-Alaska) for voting against it. (Reuters)

Surprise! The most likely option to revive Obamacare repeal isn't to repeal it at all.

Republicans tried for months on their own, couldn't do it, and now some key GOP lawmakers are advocating for the opposite approach. Democrats, meanwhile, have signaled they're open to renegotiating parts of Obamacare (so long as the intent isn't to repeal it). House Minority Leader Nancy Pelosi (D-Calif.) sent a letter Friday to Republican leaders extending “the hand of friendship” on reforming health care, specifically stabilizing the health-insurance markets so more insurance companies join the exchanges and finding ways to lower premiums for middle-class families.

There's a growing consensus among GOP members of Congress that working within the confines of Obamacare may be the only way to fix what they see as wrong with the law:

“What have we to lose by trying to work together to find those solutions?” McCain said days before he helped end Republicans' last best chance to repeal Obamacare. “We’re not getting much done apart.”

"[Bipartisan debate is] how we get the best legislation,” Sen. Susan Collins (R-Maine) said Sunday on NBC's “Meet the Press.”

But: Talking about compromise and actually finding compromise on something as polarized as health care are two very different things. Which is why Congress's most likely option to revive a health-care bill still is far from a sure thing.