What branch of government was most exposed in the recent events in Washington ? How can a situation like that be avoided?

The legislative branch. That includes Congress (House of Representatives, and the Senate).

Explanation:

A situation like that can be avoided by the security not letting the people into the building, and law enforcement taking the social media posts seriously taht had been discussed for at least a week in advance, even tweeted by Donald Trump.

answer; a team- maintenance role;

answer; coal reserves in the u.s are far greater than petroleum reserves;