While the Constitution guarantees the right to assemble and protest peacefully, it does not guarantee the right to become violent with intent to destroy property or injure and kill people.
What happened at the Capitol Building was not a peaceful protest, but an angry, violent mob bent on causing mayhem and destruction to interrupt the legal duty of Congress to certify an election.
President Donald Trump encouraged and instigated thousands of his supporters to march on the Capitol to vent their anger about these proceedings, since he still was insisting that the election was stolen from him.
The lawsuits the president's lawyers filed were all found baseless and dismissed by the courts, yet the president continued to adamantly insist that there was fraud.
Why was there a lack of adequate security, which certainly made it so much easier for the angry mob to force its way into the Capitol? Officials knew for days that these protestors would be coming.
Despite this dastardly attempt to disrupt our government, it failed and democracy prevailed.