May gives Putin til midnight to answer questions on poisoned spy:
On Monday, May said it was "highly likely" that the government of Russian President Vladimir Putin was responsible for the poisoning Sergei Skripal, a former Russian double agent who passed secrets to the U.K., and his daughter, Yulia.
May then gave Russia until midnight Tuesday to explain why a Soviet-developed nerve agent was used in Britain.
"Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian state against the United Kingdom," she said, promising "much more extensive measures" than the U.K. has previously taken against the Kremlin.
So what are May's options — and how could they affect the U.K.'s closest ally, the United States?
Perhaps the most drastic possibility is that May might invoke NATO's mutual defense clause, Article 5. The first and only time this has been used was by President George W. Bush after the 9/11 attacks on the United States.