Why the Senate election map is so bad for the Democrats

The Democrats have a good shot at winning a majority in the House this November, and now there's even talk of the Senate being in play — but this chart shows why that's such a long shot.

Reality check: It would take a tsunami, not a wave. Of the 35 seats up in 2018, 26 are held by Democrats or independents who caucus with the Democrats. And 10 of them are up for re-election in states won by President Trump in 2016, while Republicans only have to defend one seat in a state won by Hillary Clinton.

How to read this chart: Each rectangle is a senator up for election in a given year. Seats on the left side of the chart are seats in states carried by a Democrat in the previous presidential election. Seats on the right side were last won by a Republican. The dots inside the rectangles indicate seats that changed parties in the election.

What to look for in the chart:

• 2014: Republicans flipped every Democratic seat in a red state and picked up two more seats in states won by Barack Obama in 2012.
• 2008: Democrats picked up eight seats — the largest single-year gain for Democrats since 1986.
• 2004: The last time Democrats defended 10 seats in red states — they lost six of them.
• 2000: The GOP held 13 seats in blue states and wound up losing six.