Why it's so hard for Democrats to win the House

Vox reports:

Since the 2010 elections, Republican control of the House of Representatives has been the biggest obstacle for progressives trying to pass new laws. Democrats have longed to retake the chamber, and with historically low congressional approval and bad Republican favorability ratings, some now hope that their party's 2016 presidential nominee will be able sweep them back into control.

But it doesn't look likely that the GOP House will go away anytime soon. Democrats currently need to pick up 30 seats to retake the House, and there's little historical precedent for such a wave helping out the president's party. Indeed, no incumbent president's party has managed to achieve such gains since Lyndon Johnson's historic 1964 landslide.

The odds.