From a Republican 'tsunami' to a 'puddle': Why the forecast for November is changing

For political professionals in both parties, that's the capsule explanation for why the Democratic position in the midterm elections appears to have improved so much since summer began.

When the election looked to be primarily a referendum on the performance of the Democrats who control the White House and Congress, Republicans were optimistic that a towering "red wave" would carry them to sweeping gains in November.

But with evidence suggesting more voters are treating the election as a comparative choice between the two parties, operatives on both sides are bracing...