Well, no. For a lot of reasons.
Before we get into the important question of the mechanics of having 650 million people roll up to enter the United States, an exercise that will hopefully make clear just how hyperbolic this particular schmear of hyperbole happens to be, let's stop and consider the comment. Donald Trump uses hyperbole the way some politicians use touching voter anecdotes — to reinforce a broader political point. He says completely outrageous and completely untrue things because he feels as though they bolster his broader point: Immigrants are risky. Is it true? Not the point. The point is oh no, immigrants.
This particular claim turns his normal immigration hand-wringing upside down. Usually he wants to curtail new immigration because, in his formulation, scattered among the some-of-them-who-are-good-people are a number of ne'er-do-wells who bring drugs and commit crimes and are adherents of the Islamic State. He's repeatedly pledged that "the good ones" could leave the country and come back, as a sop to those who criticize him for rejecting new immigrants out of hand. The "650 million" claim is a warning about having too many "good ones." It's a parent's warning about taking it easy on your Halloween candy, except the warning is that if you eat all your candy in one night and all the leftover candy in the house and also eat all of the candy collected by every kid in the tri-state area and also have a fudge IV inserted overnight, you will get sick.
So: 650 million people! That's a lot.
The population of the planet is about 7.1 billion, meaning that Trump figures one out of every 10 citizens of the world wants to live here for some reason. (About 319 million already do.) The United States would jump from the third-most populous country to ... the third-most populous. (China and India are very big.)
Where would those people come from? If literally every person in South America suddenly decided that Reno was a more appealing place to live than Rio, we could see 422 million people slowly make their way up to the United States. Add in everyone from Central America and we're at nearly 600 million. If every Canadian decided to move south, we hit 633 million, still a bit short. If every non-American in the Western Hemisphere decided to move to the United States, we'd be talking about 677 million people.
Let's assume that most of the new immigrants Trump is warning about are coming from Central and South America. (He seems less concerned about Canadian immigration, downplaying the need for a wall that the Trudeau administration would pay for.) That means they can simply pack up cars or trucks with their belongings and head on in. After all, Trump's argument is that the Clinton administration would welcome them; there's no need to trudge through the Arizona desert to enter the United States if you're allowed to come in.
The Department of Transportation has data on the number of border crossings each month. In July, 12.7 million people crossed the Southern border in personal vehicles or in buses. Six million crossed the border in Texas; 4.9 million in California and 1.5 million in Arizona. So far this year, 83 million people have crossed the border with Mexico.
Trump sort of paints himself into a corner with the "in a week" part of his comment. If we're assuming that all 600 million people from Central and South America want to relocate to the United States in a week, it would mean that each of the 25 busiest border crossings with Mexico would need to operate at 44 times the weekly capacity during July of the crossing in San Ysidro, Calif., the crossing that currently handles the most traffic. All moving in one direction, mind you; the Border Patrol would probably need to put the kibosh on anyone wanting to head south during that week. Or, of course, people could rent all-terrain vehicles and head across the border willy-nilly. With that backlog at the border crossing, it would be tempting to skip the wait. And this only accommodates 600 million people.
How many cars are we talking about? Let's assume that we squeeze four people and their belongings into each car. (That's higher than the average crossing the border; in July, most crossings had an average of two people in each passenger vehicle.) The most popular car in Brazil is the Fiat Palio, each of which is at least 12 feet long.
The line of Palios carting all of the new immigrants into the United States would therefore be 1.8 billion feet long, enough to stretch around the Earth 86 times. If each car started in Panama City, Panama, it would mean 106 lanes of traffic heading up to El Paso, with no room between the cars' bumpers from the Texas border to the Panamanian capital.
If everyone in Central America, South America and Canada came to the United States, 17 million more would have to come from somewhere else, meaning that they'd have to either fly or take a boat. (Of course, a lot of the 600-plus million who came from Central and South America would skip the thousands-of-miles-long line of cheap Italian compacts and fly or sail themselves.) The busiest airport in the country is in Atlanta, where just under 2 million people flew in and out in an average week in 2015. So we'd need nine airports to handle an equivalent capacity in this mega-week of immigration, just to accommodate those 17 million extra people.
If more of those new immigrants to the United States wanted to fly here, we've got a bit of a problem. The top 45 busiest airports in 2014 handled an average of 24.8 million people a week in 2014. If each of them somehow magically were able to deal with 10 times their normal influx of passengers — allowing flights at all hours and allowing planes to land in much closer sequence, say — we'd hit less than half of the one-week immigration total that Trump foresees.
Immigrants hoping to come by boat have a few options. If they're coming from Cuba, say, any number of boats might work. If they're coming from Europe, Africa or Asia, they need something a bit more robust. The largest cruise liner in the world is the Harmony of the Seas, which carries 5,500 passengers in luxurious comfort. If those 17 million people wanted to cross the ocean on a fleet of Harmony of the Seases, we'd need 3,090 of them. If my math is right, they'd displace a collective volume of about 100,000,000 liters of water (assuming a weight of 71,500 tons apiece). The good news is that the oceans are large enough to handle the slight rise in ocean level that would result.
Once all of these immigrants arrive that week, there would be a lot of ancillary problems. Traffic coming away from the borders and airports would be a mess for a long time. There were about 2.2 million rental cars in the United States in 2015; it's safe to assume that many rental car companies would be out of inventory for a while.
Another complication is housing. The Census Bureau estimates that there are currently 17 million vacant housing units in the country, meaning that the new immigrants would have to squeeze 38-to-a-home on average. We can offset that a bit by filling up each of the 5 million hotel rooms in the country. But that only helps a little.
I guess what I'm trying to say is that even if Hillary Clinton wanted to allow a tenth of the world to move to the United States, which she doesn't, it couldn't really happen, even if you gave her more than a week to get the job done.
It's almost like ... maybe ... Donald Trump just says things for effect sometimes?