This scenario involves Republicans resiliently holding on to both chambers of Congress.

For this to happen, the polls - which have previously underestimated Trump's support - need to be wrong and the toss-up races to mostly fall the way of Republicans.

Not only would Republican voters have to turn out in unexpectedly impressive numbers, independent and Hispanic voters who had seemingly soured on Trump's policies would have also to break his way in the end.

In this scenario, control of the House, far from being a done deal for Democrats, could end up coming down to California and its extended days-long counting process for mail-in ballots.

In the end, Republicans might eke out a slim overall majority thanks in part to efforts to draw more favourable congressional district lines in places like Texas, Florida and North Carolina.

It could also be that Republicans win all the Senate contests in the conservative states and they also flip Michigan, a seat that was held by Democrats heading into the vote.

Even if Republicans don't hold North Carolina or win in Democratic-controlled Minnesota or New Hampshire - races just on the periphery of competitiveness in this year's elections - they may at least make the Democratic candidates sweat.

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