Conversation so far:
When did Paul Ryan run for speaker of the house?
Ryan confirmed on October 22, 2015, that he would seek the speakership
What policies did Paul Ryan help implement?
Ryan supported tax cuts including eliminating the capital gains tax, the corporate income tax, the estate tax, and the Alternative Minimum Tax.
Can you tell me more about Paul Ryan's bid for the seat?
Ryan, upon confirming his bid for the speakership, stated, I never thought I'd be speaker.“

Question: Why did he resign?
Self-contained rewrite: Why did Paul Ryan resign?