A heated argument in the West Wing between chief of staff John Kelly and national security adviser John Bolton over a recent surge in border crossings turned into a shouting match Thursday, two sources familiar with the argument told CNN.

The exchange lay bare a bitter disagreement that has existed between two of President Donald Trump’s top aides for weeks now. Trump, who was incensed about the rising levels of migrants and threatened to shut down the southern border on Twitter earlier that morning, took Bolton’s side during the argument…

The fight between Kelly and Bolton startled several aides throughout the West Wing on Thursday, a person who heard the shouting said, adding that the raised voices went well beyond the heated discussions of the Trump administration.