Answer:
(A) “What happened here today was an insurrection, incited by the President of the United States," said Mitt Romney.
Step-by-step explanation:
That was the sentence to support the authors claim about the attack on Capitol threatening democracy. This is because, it has always been the traditions for decades for law makers to gather in Capitol to rectify the delegate votes and assert who becomes recognised officially as the president.
For protesters to attack the law makers in that chamber while trying to prevent them from carrying out their consitutional rights shows the threat to democracy being practiced in their country.