Article II Section 4 of the Constitution states that Bribery is a reason for impeachment and removal from office for all Civial Officers of the United States
The Supreme Court of the United States in "Citizens United" found that corporations could give/donate unlimited funds to the campaign funds of members of congress.
However, as of recent, those "generous donations" have been used as a threat against members of congress in order to achieve passage of legislation. They call it "Primarying". This "quid pro quo" constitutes Bribery or coercion. According to law, the offerer and acceptor of a bribe are both guilty of Bribery. Therefore anyone voicing or implying a threat of primarying is a Briber; such as: Steve Bannon, Grover Norquist, Koch Brothers, Mitch McConell, Paul Ryan and others.