By Phil Mattingly, CNN

(CNN) -- A bipartisan health care deal, announced by Republican leaders Tuesday and long negotiated between Sens. Lamar Alexander and Patty Murray, has been reached.

The question now is can Alexander, a Tennessee Republican, and Murray, a Washington Democrat, whip the support to actually force leaders to consider the measure to fund the cost-sharing reduction payments to insurers for two years and increase state regulatory waiver speed and flexibility. The short answer to this: they've got a long way to go.

The key to all of this: President Donald Trump. Period. And he just dropped a bomb on this whole process with this tweet:

"I am supportive of Lamar as a person & also of the process, but I can never support bailing out ins co's who have made a fortune w/ O'Care.

Here's why: If Trump got fully behind this and explicitly told House and Senate leaders this needs to be taken up, it's a potential game changer. Doesn't guarantee it, particularly given conservative opposition, but certainly would be a huge step.

But even before the tweet, he was trending in this direction of opposition, according to several sources. His support, or wavering support, or potential outright opposition over the course of just hours yesterday left everyone without nobody has any clear idea where Trump stood.

Well, now you know. And here's how it came to be: Behind the scenes, conservatives -- including some lawmakers -- flooded the White House with concerned calls and messages Tuesday night. They are deeply opposed to the deal, and top conservative advisers to the President, according to multiple sources, are as well.

The POTUS evolution:

Trump's evolution on this issue over the last five days has been nothing short of jaw dropping.

He:

• Repeatedly publicly touted bipartisan talks (which, while he never explicitly detailed them, were always assumed to be the Alexander-Murray talks)

• Behind the scenes, told Alexander in several personal phone calls that he not only supported what he was negotiating, but urged him to reach a final deal. In fact, Alexander told CNN Tuesday Trump's personal urging was crucial to reaching a deal.

• Appeared to explicitly endorse the deal when asked, specifically, about the deal, in his news conference Tuesday

• Then he appeared to pull back Tuesday night at his Heritage Foundation speech. It was subtle, but immediately read by conservatives already opposed to the deal is a crucial sign, one the White House had been advising them was coming, according to several sources.

"I'm pleased the Democrats have finally responded to my call for them to take responsibility for their Obamacare disaster and work with Republicans to provide much-needed relief to the American people. While I commend the bipartisan work done by Sens. Alexander and Murray -- and I do commend it -- I continue to believe Congress must find a solution to the Obamacare mess instead of providing bailouts to insurance companies."

So where does that leave us:

All eyes on now remain on Trump -- he's taken about 6 different positions on this in the last 18 hours, so even though the tweet was about as unequivocal as it gets, who knows where he'll end up.

But also Senate leadership. And members of the House. And other Senate Republicans. In other words, the deal was but one piece of a very complicated, possibly impossible to complete, puzzle. We're at the opening stages of this.

In the meantime: Alexander was very clear Tuesday. His focus is all about getting co-sponsors for the bill. Details were sent to GOP offices last night. Staff was briefed as well. The best path forward for this bill, in one form or another, is if Alexander and Murray are able to construct significant, unequivocal bipartisan support. Essentially, force the hands of GOP leaders. Again, it's a long road, but that's the focus and the goal. As one GOP aide supportive of the deal put it, acknowledging that there's a tough road ahead: "It's a step by step process. One foot in front of the other at this point."

What to watch today:

• The President, and anything more he has to say about this

• Where GOP senators stand

• Any more reaction from the House Republicans

Where the House is on the deal: As Senate GOP leaders gauge the temperature of their conference, they are keeping a close eye on the House. There is zero -- zero -- appetite to take a vote on something that sustains Obamacare if it doesn't have a future in the House. And as it currently stands, large chunks of the House GOP conference are opposed to the idea.

"A majority of our guys don't one this," one House GOP aide said. "Didn't want it before, don't want it now. They didn't come here to fix Obamacare."

Key reality checks to keep in mind

Reality check #1: If this deal was put on the Senate and House floors as a standalone measure, it would likely easily have the votes to pass.

Reality check #2: For GOP leaders, the above is not the metric for whether something gets to the floor. They represent their respective conferences, and if those conferences reject the idea out of hand (which is possible, and even likely, in the House), the leaders will follow suit.

Reality check #3: There's not a lot of time or bandwidth to take this up as a standalone bill. In fact, even the sponsors are aware that is probably unlikely. The way -- and at this point, seemingly the only way -- this deal is signed into law is as part of a broader package. So keep a close eye on potential vehicles to attach the deal to as an amendment. Democrats have already said the CSR payments need to, at the very least, be in the end-of-year spending bill.