The highest court in the UK says Theresa May's government must go through Parliament to formally trigger the two year exit from the EU.
Why it matters: It could spell delay, delay, delay. May said last week that she'd give Parliament a vote on the final terms of Brexit. Now she'll need their approval to start those negotiations.
Even still: Jeremy Corbyn, the leader of the opposition, says he won't block Article 50.
What to watch: May visits the U.S. later this week, meeting with Trump — a very public Brexit supporter — on Friday.