The Senate is about to vote on the future of NSA spying. Here's what you need to know.

The original version of the USA Freedom Act, introduced by Rep. James Sensenbrenner (R-WI) in October 2013, had a number of provisions on the wish lists of civil liberties groups. But by the time the legislation was approved by the House of Representatives in May 2014, it had been watered down so much that leading civil liberties groups opposed it.

So, in July, Sen. Patrick Leahy (D-VT) introduced his own version of the USA Freedom Act in the Senate. It is less radical than the original USA Freedom Act, but...