“Repeal and replace” prevailed as the GOP mantra on health care reform dating back to the Pleistocene Epoch, wedged somewhere between the Pliocene and Holocene periods.

“Repeal” had never been much of an issue for Republicans. However, the devil burrowed into the details of “replace.” Still, Republicans clamped the alliteration together in a binary conjunction.

That was until President Trump attempted to decouple them Friday with a breakfast-time tweet.

“If Republican Senators are unable to pass what they are working on now, they should immediately REPEAL, and then REPLACE at a later date!” the president tweeted.

If it were only that easy.

A December 5, 2016, memo from Heritage Action outlined a potential path for Republicans to ditch ObamaCare and concoct another health care plan down the road.

“Some will argue that we have a replacement plan at the same time as repeal, but they make this argument hoping to kill the momentum for repeal under the guise of repeal and replace.

However, until we fully repeal ObamaCare, Republicans will have a difficult time agreement on a combination of replacement packages,” read the memo for Heritage Act, the conservative Heritage Foundation’s political arm.

This wasn’t a desire to dissolve ObamaCare in an instant. There could be sunsets and other caveats to avoid chaos in the shift. Instead, isolating repeal from replace could serve as a fulcrum against which to accomplish the second goal. It would pressure Republicans to find a health care solution that has eluded them for years.

Back in December, Heritage Action hoped Congress would finish the replacement bill by the end of this year and begin implementing the new health care law in 2018 and 2019.

“This would ensure that individuals who have purchased plans through the Obamacare exchanges have ample time to transition into the private sector or employer provided coverage,” Heritage Action wrote.

The missive concluded with this gem:

“There are no procedural excuses for not moving forward. The only reason for delay and inaction would be an unwillingness to deliver on a six-year-old promise to fully repeal ObamaCare. There are no more excuses.”

And here we are.

There’s no obvious breakthrough on health care coming right away, even though some thought a “deal” might emerge magically at 5 p.m. Friday.

David Popp, a spokesman for Senate Majority Leader Mitch McConnell, R-Ky., says, “discussions continue within the conference. I’m sure we’ll be having lots of back and forth with CBO (Congressional Budget Office in the coming weeks. But no announcements for you yet.”

Underscore the “coming weeks” part of Popp’s quote as McConnell dispatches retooled proposals to the CBO in an effort to court recalcitrant Republicans.

But if that fails, a senior White House source tells Fox News colleague John Roberts that President Trump wants to bifurcate repeal from replace. The assertion is that the House and Senate previously voted to repeal. So why not just cleave the two -- perhaps to turn up the heat on Republicans -- and get somewhere.

But this ploy imposes problems.

Many on Capitol Hill suggest that a full-blown repeal without an immediate fallback would infuse fear and confusion into the marketplace among insurers and consumers.

That’s to say nothing of the financial markets. If there’s anything people want, it’s stability. Not knowing if anything comes next is an issue. House Speaker Paul Ryan, R-Wis., said long ago that the system cannot just revert to the pre-ObamaCare age.

Secondly, a stand-alone ObamaCare repeal would presumably include a sunset -- most likely after the 2018 midterms or even the 2020 presidential election. It’s hard to pivot quickly. Plus, a grace period allows lawmakers and Trump to dodge political fallout.

However, would a solitary ObamaCare repeal impose some sort of an “enforcement mechanism” to compel lawmakers to enact a replacement before the clock ran out? Maybe. But previous efforts to coerce lawmakers to settle other issues failed spectacularly in recent years.

To wit: The federal government is now into its sixth year of budgetary sequestration -- a set of mandatory spending cuts imposed on Congress, by Congress.

Sequestration is the consequence of an aborted endeavor to slash $1 trillion in spending in accordance with the 2011 Budget Control Act (BCA) that raised the debt ceiling. Sequestration was an onerous penalty Congress would pay should a select cohort of lawmakers -- appellated as “the supercommittee” -- stumble to forge an agreement. Nobody wanted sequestration. Most people were convinced the super-committee would succeed.

It didn’t.

Sequestration remains in place today, running until at least the mid-2020s.

It’s unclear if the House and Senate could now pass a detached ObamaCare repeal bill like Republicans did in 2015.

One issue could be the Senate. The chamber would likely mimic its 2015 repeal effort through a process called “budget reconciliation.”

The process shuts off Senate filibusters. Otherwise, Democrats would inevitably block the bill, stifling Republicans. So budget reconciliation is the way to go.

But the process has its own issues. An ObamaCare repeal lifts all sorts of taxes. Federal revenue could drop, hiking the federal deficit. That could run afoul of strict budget reconciliation rules that require bills be budget neutral. The lost revenue could be trouble. But Republicans crafted the 2105 ObamaCare replacement bill in a way that met budget reconciliation strictures.

The bigger issue may not lie in how the GOP replicates its 2015 tactic. The circumstances are different this time. Unlike two years ago, a vote to repeal ObamaCare would be real.

The 2015 ObamaCare repeal votes in the House and Senate were artifice. Republicans finally got to deposit an ObamaCare repeal bill on the president’s desk because it marked the first time the GOP held the House and Senate since the legislation became law.

But there was a fait accompli. Naturally, then-President Barack Obama would have vetoed the repeal measure. And he did just that.

Everyone knew the endgame -- just as they know the endgame now.

The difference now is that Trump would sign the bill.

That’s good news for cngressional Republicans. But it scares the dickens out of many others. They fret they’ll never reach an agreement on an adequate ObamaCare replacement bill.

Some lawmakers may simply refuse to vote yes unless GOP leaders buckle repeal to replace. That could imperil the chances for passage.

Certainly the president and GOP congressional leaders could remind Republicans they already voted to repeal.

In the Senate, Sen. Susan Collins, R-Maine, is the only sitting GOPer who voted nay. But things are different this time. Under Trump, an ObamaCare repeal would be real -- regardless of the ramifications.

Speaking on Friday night in Elizabethtown, K.Y, McConnell rejected the president’s Twitter entreaty. The leader said, “We are going to stick with (the current) path.”

Republicans used talk of repealing ObamaCare as a powerful political weapon with which to bludgeon Democrats. Now Republicans are trying to make good on their own promise. The GOP always viewed repealing Obamacare as the easy part. But now, a simple repeal is more challenging.