Here's the thing. Panama is an ally. They continue to work with SouthCom, and the DEA closely. Panama is also the central international banking resource for money laundering. The whole taking the canal back stemmed from the death of President Carter, and the usual suspects grousing about our living up to our end of the treaty, and handing it over to Panama in 1999.
I doubt it will happen, but in three weeks Diaper Donny has set back US-Central American relations almost 30 years.
As far as taking the canal by force goes, I happen to know a lot about Operation: Just Cause. Can we do it? Sure. Will it be as easy as 1989? Hell no. In 1989 we had bases in Panama, with the 193rd Airborne brigade, and a few thousand US Marines, and 7th Special Forces Group already in place as residential units. They lived and trained in Panama, and worked with their PDF counterparts. For the invasion there were a total of 27,000 soldiers, a ratio of 3 to 1 against the PDF. Almost 5,000 of them had been sent down to Panama from Fort Ord and Fort Bragg in October, 1989. It would be the same as if we wanted to capture the state of Georgia today with Fort More, Fort, Fort Stewart, Robins AFB, Moody AFB, and Kings Bay as forward staging areas. It would be a short battle.
Today we have no bases in Panama. The PDF like any other Central American military force, mildly capable, but no match for even our National Guard. And in theory 7thSFG and SEAL teams could infiltrate the canal zone to prevent sabotage ahead of the invasion force (as they did in 1989). The problem with Panama is the jungle. Most Vietnam vets who fought in Just Cause, or just did Jungle School at Ft, Sherman said the jungles there are worse than SE Asian jungles. In 1989 the PDF didn't put up much of a fight because they didn't want to die at Christmas for Manuel Noriega. And because we had relationships with many PDF officers and NCOs we were able to call them on the phone, and ask them to surrender instead of getting killed in battles they would lose. The hard fighting was over in 11 days, the canal zone was under US control in under 20 hours. And unlike Iraq, we put the PDF back into operations, and returned their weapons, and they worked with our forces to chase down Noriega loyalists, and Cuba spies.
The problem with Just Cause is we made it look easy, and it set up Operation Desert Storm, and the legacy of armed intervention ever since. But to date there has been almost no analysis of the invasion beyond a few books (which I own all) and a Rand Corp study. No asks what would have happened had the PDF and Dignity Battalions ( Panamanian Fedayeen, sort of like making the Bloods and Crips into the National Guard) had gone into the jungles to fight us? We were down there from October, 1989 through February, 1990. Had the resistance gone into the jungles we would have been fighting in Panama for at least three years. In 1989 we killed fewer than 500 Panamanians. Any future invasion will kill thousands (potentially) depending on where the fighting occurs. Panama City has tripled in size, vertically and horizontally. We can't assume foreign fighters won't show up in such an operation today.
I doubt China would intervene, but they sure might use our invasion as cover to take Taiwan. We would instantly be at a disadvantage, certainly from a place of credibility as we would be guilty of doing the exact same thing to Panama - taking back something that used to belong to us decades ago. It would be a recruiting poster for anti-American entities worldwide. There is no need for this action. Panama has made no threats. We've reelected a moron.