[justlurking]

But also keep in mind that a sizable number (10, I think) of the 23 Democratic seats up for election in 2018 are in states that Trump won in 2016.

Historically, the party in the White House loses seats in the mid-term election.

In 1994, it was enough to put both the House and Senate back in control of the Republicans, for the first time in decades. It happened again (for the Democrats) in 2006, and again (for the Republicans) in 2010.

The map may appear to favor Republicans, but it may be the Democrats ready to crawl over broken glass to vote against Trump's agenda.

If Republicans aren't satisfied with Trump's progress, they may stay home.

[HiTech RedNeck]

The difference this time, perhaps, will be that there will be a live wire in the White House, not a flat tire. He ought to be watching for ways to guard his Congress, and likely will.

[Alberta's Child]

All of that is true. One thing to keep in mind is that some of these major transformations (including the 1994 landslides for the GOP) were driven by demographic shifts and re-apportionment of Congressional districts after the most recent census.

When I have time I am going to back and research this, but I suspect this country has seen more dramatic shifts in Congress early in a decade than later in a decade.