Full Video: Impeachment Managers Show New Graphic Security Footage Of Ca...

It doesn't look too dangerous for those police on the barrier until you realize that they were about to be surrounded.  Once surrounded by a mob, they were very likely to lose their weapons making the crowd even more dangerous than they already were.  They had no choice, under the dangerous conditions that were developing, but to pull back and flee.  They had to keep themselves safe but; even more importantly, they had to keep their own weapons out of the hands of the mob.  The only way outnumbered police can secure their weapons is to withdraw to a defensible position and do so with all haste.

REMEMBER ME???

RUNNING FOR OFFICE???

TRAINING DAY AT THE CAPITOL?

The Sedition Act of 1918 (Pub.L. 65–150, 40 Stat. 553, enacted May 16, 1918) was an Act of the United States Congress that extended the Espionage Act of 1917 to cover a broader range of offenses, notably speech and the expression of opinion that cast the government or the war effort in a negative light or interfered with the sale of government bonds.[1] It forbade the use of "disloyal, profane, scurrilous, or abusive language" about the United States government, its flag, or its armed forces or that caused others to view the American government or its institutions with contempt. Those convicted under the act generally received sentences of imprisonment for five to 20 years.

https://en.wikipedia.org/wiki/Sedition_Act_of_1918