Answer: Depending on your point of view, there are different situational ironies: In brief:
Claim: The situational irony is that the place where American democracy is carried out became the site of an undemocratic mob disrupting the process of counting votes, the instrument of democracy.
The US Congress and Senate are democratically elected representatives who make the laws on behalf of the people of their states. They were engaged in a legal process of counting the Electoral College votes for president and vice president when the mob of protestors invaded the Capitol and disrupted the process.
Reasoning: The United States Capitol Building is a symbol and the center of American democracy, but the actions of the protesters claiming to be patriots were undemocratic. They sought to use their force rather than democratic voting to get their way to keep President Trump in office.
Alternatively:
The situation is ironic because the protestors interrupted and prevented the very debate which may have given voice to their claimed grievances that some of the states had changed their voting procedures and some votes were not legitimate. (Despite there being no evidence of substantial fraud found by any stare officials or courts)
The Senate was in the process of debating the legitimacy of the electoral votes from Arizona then the proceedings were halted for security reasons to protect the senators when the protestors had invaded the Capitol.
The U.S. Capitol which is supposed to be one of the most secure buildings in the nation was invaded by its own citizens who claimed that the election results were fraudulent, and prevented the senators and representatives who were planning to debate those claims from making their cases. Their breach of security led to the end of their own cause.
