Bribery and quid pro quo are pretty much the same thing.
Um, no. Bribery is to entice someone with money or something of value to do something dishonest or illegal. Quid Pro Quo is I'll do you a favor if you do me a favor. Extortion, which is also being bandied about, is compelling someone to do something with the threat of force or injury used as the incentive.
Then there is the far more common "making a deal" business which happens billions of times every day. An employer/employee relationship is an example. I pay you to do a legal job for me.
Should the U.S. just give millions/billions of dollars to another country with no strings attached? If there is corruption, whether by the host government or one of our own government officials, is it illegal to investigate it?