It takes longer than everyone predicted, new potential issues will rise and fade by the hour, and eventually, arduously, an agreement to avert another shutdown will be reached -- or at least that's the plan.

Republicans and Democrats are still trading proposals. Earlier this week, it was at the staff level, then at the subcommittee chair level and now it's at the highest level. Multiple people involved say things are still clearly moving in the right direction, but get ready to start hearing this quite a bit over the next 24 hours: "Nothing's agreed to until everything's agreed to."

Bottom line

Negotiators were pushing for a final agreement by Friday night, but people involved now say that's unlikely at this point. That's not because there are significant new problems, but because hashing out the final details on complicated (and politically divisive) issues takes time.

"Things are definitely still on track," one source involved said Friday morning. "But we've still got a lot of work to do."

Timeline

Lawmakers on Thursday said the goal was to finish things up early this weekend in order to draft the actual legislation and have it posted by Monday. That would tee up House votes later on Wednesday, with the Senate moving immediately after.

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The President

By far the largest outstanding question throughout the negotiations has been where President Donald Trump, once dismissive of the talks altogether, would end up if an agreement was reached. There was, and remains, real trepidation the President will simply reject the agreement and leave lawmakers with no Plan B.

But Republicans were buoyed by Senate Appropriations Chairman Sen. Richard Shelby's presentation behind closed doors after his visit to meet with the President. It was positive, multiple senators in the room said, and most were left with the impression Trump would come on board with a final agreement.

"The President was urging me to try to conclude these negotiations. This is the most positive meeting I've had in a long time," Shelby said after he returned from the White House. "So, we're not there yet, we're seriously negotiating."

The reality

Trump, should congressional negotiators reach a final deal, is going to be jammed. To some degree, that's by design -- the push by congressional leaders in both parties has been to let the conference committee, and then the whole Congress, work its will. In other words, take it out of Trump's hands, or tweets. Combine that with the growing opposition among GOP senators to any emergency declaration and there's a cautious sense on Capitol Hill that Trump will have to sign

"I'm not going to predict what he'll do," one Democratic senator told me. "But if we've teed it all up for him to sign and get it off his plate, I'm not sure there's anything else he can do."

The senator then paused, chuckled, and said: "But honestly, who the hell knows."

Something to keep an eye on

Several negotiators and people involved in the talks have made clear that some form of border barrier will be in the final agreement. The final funding number and the actual design of the structure, however, is still under negotiation, though Democrats make clear there will restrictions on what can be built -- and where.

"Like in anything else, it's a tradeoff," Rep. Lucille Roybal-Allard, a member of the conference committee and the leading voice for House Democrats on the DHS funding proposal, told reporters Thursday.

Roybal-Allard, D-California, said Democrats were "waiting for a counteroffer right now, and when we see that, I'll have a better idea of how close we are. "

But the existence of any funding for barriers at all will complicate the votes of a number of Democrats in the House and, it should be noted, several Democrats in the Senate who are, or may soon be, 2020 presidential candidates.

The existence of new funding for personnel beyond customs agents, or detention beds, would also be a dealbreaker for some, including more than 20 members of the Congressional Hispanic Caucus, and new freshmen progressives like Reps. Alexandria Ocasio-Cortez, Ilhan Omar, Ayanna Pressley and Rashida Tlaib.

To be clear, aides don't expect those potential "no" votes to endanger any agreement, but it underscores the complicated balancing act negotiators face on an issue that creates sharp divides in the Democratic caucus.

Another looming potential issue

Disaster aid. It's been in and out of the funding negotiations for months, and is exceedingly important to several delegations (and as such, voting blocs). That said, there are disagreements between House Democrats and Senate Republicans on the scope and scale of any disaster supplemental. How that is addressed -- or if it's addressed at all -- will be something to watch in the days ahead.