On Monday, a bipartisan group of senators unveiled a proposal to revamp the nation's immigration laws. Among other things, that would include an eventual path to citizenship for most of the nation's undocumented immigrants.

So how many people would that affect? At the moment, there are roughly 11.1 million undocumented immigrants residing in the United States. Yet it's worth noting that this number has dropped sharply during the recession, as this chart from Pew Research Center shows:

The key reason for the drop is that overall Hispanic immigration from Mexico and Latin America has slowed significantly since the financial crisis hit. And there are multiple theories for why that is:

Demographers say illegal Hispanic immigration — 80 percent of all illegal immigration comes from Mexico and Latin America — isn't likely to approach its mid-2000 peak again, due in part to a weakened U.S. economy and stronger enforcement but also a graying of the Mexican population.

A key question here is what happens as the U.S. economy recovers. If the recent plunge in illegal immigration was simply due to a dearth of jobs in the United States, then the influx of undocumented workers should soon pick up again.

On the other hand, if the decline in illegal immigration since 2007 has been driven by changes in Mexico and Latin America — older populations, stronger economies — then we might not see as big a rebound in the years ahead. At least some demographers support this second theory. As the Pew Research Center's Jeffrey Passel told the AP last month, "We are not going to see a return to the levels of Mexican unauthorized immigration of a decade ago."