What is quid pro quo and does it matter?

What’s happening

Quid pro quo. Quid pro quo. Quid pro quo. A phrase that was previously unknown to anyone who wasn’t a legal expert or Latin enthusiast suddenly seems to be the most important three words in America.

The impeachment inquiry into President Trump has brought the saying — which translates as “something for something” — into the popular lexicon. At issue is whether Trump should be impeached for withholding $391 million in aid money (the quid) in order to compel Ukraine to investigate the business dealings of Joe...