He saw the handwriting on the wall

There goes another Republican. And thank heaven for this one.

House Speaker Paul D. Ryan (R-Wis.) has told friends, colleagues and staff that he has decided not to seek reelection this year, according to several people familiar with his plans, adding to the uncertainty about whether Republicans can maintain control of the House.

A Republican close to Ryan said he plans to serve out his term and stay on as speaker for the remainder of the year.

  WaPo

Another chicken Republican who doesn't want to go out losing an election.

Applause could be heard outside Ryan’s office shortly before 9 a.m. as he was meeting with staff.

As an appreciation for his time there or because he's leaving?

The party has seen a large number of retirements, and Ryan’s exit is certain to sap morale as Republicans seek to contain a surge in enthusiasm from Democrats, whose fortunes have been buoyed by the unpopularity of President Trump.

[...]

If he sticks to this plan, Ryan will become the first speaker since Democrat Tip O’Neill in 1986 to announce his retirement so far in advance. Some of Ryan’s close friends believe this may be a mistake on his part.

He doesn't want to have to spend the next six months campaigning against IronStache and losing.  Ryan has made a lot of mistakes in his life. I wouldn't put this in that column.

...but hey, do what you want...you will anyway.

UPDATE: