Knock, Knock
![](https://media.wnyc.org/i/800/0/c/85/2018/10/AP_18294503072509.jpg)
Central American migrants walking to the U.S. start their day departing Ciudad Hidalgo, Mexico, on Oct. 21, 2018.
( Moises Castillo / AP Images )
( Moises Castillo / AP Images )
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