Did the Republican rumblings have at least something to do with his backing off. Or was he just doing his usual "set a fire then put it out" dance?
Just read the agreement. Mexico will take "unprecedented steps" to stop migration, which means they will deploy the National Guard across the country, they will stop human trafficking, and if any immigrants get across the US border, they will be returned to Mexico to await adjudication.
Well hell, another problem solved. This is almost as good as ending the nuclear threat in North Korea.
So far as I can tell, Trump may have finally had his first extortion success in office. Trump didn't cave, Mexico did.
Though, to be fair, that agreement doesn't really say anything other than that Mexico will deploy its National Guard to the Southern border. It mentions other things, but no actual numbers or plans, just sort of vague principles. The "to be reviewed in 90 days" part seems to be the main thing. Basically, it's an agreement to continue negotiating for 90 days.
In theory, according to the document, this would be the end of negotiations - if we presume that the measures being discussed would actually reduce the amount of immigration within 90 days. But, as said, the only explicit measure it discusses is to deploy troops to the Southern border of Mexico. That may have some effect on preventing people from coming into Mexico, but it doesn't prevent the people who are already in Mexico from continuing to head North. It will probably take a little over 90 days for those people to peter out. In the meanwhile, I wouldn't expect any actual change to the immigration numbers.
I expect that they knew that. The 90 day deadline is really a buffer for them to try and write up some actual goals - as in actual benchmark numbers - and get that down on paper. Of course, on the side of Mexico, it could just be a delay strategy while they prep to kneecap Trump.
But my guess is that they've actually caved and, having done so, they'll continue to do so. They've just decided to be Trump's chew toy, and I would expect Trump to ramp up taking advantage of them in the future.