The Democratic mayors of Denver, Chicago, Boston, and New York City were grilled for hours over their so-called sanctuary city policies at a Congressional hearing Wednesday as President Donald Trump pushes his aggressive immigration agenda and threatens to punish cities that don’t comply.

The Congressional hearing was part of a federal investigation into so-called "sanctuary cities."Committee Chairman James Comer, a Republican from Kentucky, launched the probe back in January to look into what he described as "the policies of sanctuary jurisdictions and their impact on public safety and federal immigration enforcement.

Republican members of Congress hammered four Democratic mayors about their so-called sanctuary city policies, accusing them of endangering Americans and threatening to prosecute local officials.