Some are asking, why is this caravan "Mexico's problem" to handle?
It is unquestionably Mexico's problem to handle.
It's quite simple, according to international law.
Because Mexico is the "first country of asylum" under the UNHCR (UN High Commission on Refugees) for those claiming the "need" for asylum, AND Mexico is designated as a "safe third country" for refugees seeking a "credible threat" or unsafe conditions in their country of origin.
The caravan citizens of El Salvador and Honduras cannot "skip over" Mexico to claim refugee status or make claims of asylum any where they wish-- ie, the U.S.
Mexico is not a highway. There will be serious, very serious consequences for Mexico if they do not adhere to international law. That is the leverage that both the U.N., and the U.S. bring to bear.
This is the exact same situation that unfolded in Greece in 2015 when the masses of middle east and African citizens decided to "enter" europe via Greece. Few to none of them wanted to remain in Greece, because Greece is poor, has massive financial and economic problems, and would not "provide" the generous welfare and social benefits that Germany, Sweden, and other european nations provide. So, those "migrants" REFUSED to register in Greece, so that they could continue to invade their way north to the country of their choice.
For the exact same reason Canada is sending Haitians back to Haiti who have "fled" the U.S. after their temporary protected status has ended. Canada has no obligation under international law to admit, shelter, or keep Haitians who have resided in the U.S. under a temporary program that has ended. Those Haitians who were under the temporary protected status, by the way, are free to pursue ordinary avenues for residency and citizenship in the U.S. They are most certainly "not" legal international refugees, nor are they valid asylum seekers, simply because the U.S. residency program that admitted them has ended.
None of these people have legal "right" to come to the U.S. simply because they "want" to. Let's be quite clear about that. Being a citizen of a poor country is not a "right" to force a wealthier country to let you come to live there.
What is a safe third country? - World
That said, if some of the caravan do end up at the U.S. border, I think 2 things will happen.
They will be welcomed into medical quarrantine, provided with medical care, and the children (few that there are) will be VERY well cared for-- balloons, toys, etc., while the claims of the adult/s who "brought" them are investigated and pursued. The optics will be excellent.
We may activate and deploy some domestic military resources to the border (we actually do that
very often, and it never makes the news-- there are usually lots of "full time reservists" who volunteer for those taskings), but there won't be shooting or tanks or anything that looks like "war".
The caravan participants who depart from the group and and make it thru Mexico to the U.S. border will be greeted and held in quarrantine/ detention WHILE their claims are being pursued, then most will be deported BACK TO MEXICO. Because Mexico has FORMALLY AGREED to take any caravan participants that are deported.
A tiny few of these 4000 may end up in the U.S. under some technicalities or special programs. The overwhelming majority of them will not be allowed to stay in the U.S.
The U.N. and various aid organizations will help mexico to care for whatever number of them end up staying in Mexico.