1. Could the polls be wrong?
Of course, they could. But they're probably not. Jonathan Bernstein identifies 3 risk factors for this year's polls:
"A late surge. That’s what happened in 2016: Hillary Clinton’s lead over Donald Trump fell sharply in the last two weeks of the campaign. Although the polls picked this up, or at least most of it, it’s a good reminder that even mid-October surveys can miss late change. Could it happen again? It probably won’t, but it could – in either direction. Watch what’s in the news in the final days before the election.
Luck. All polls are subject to sampling error and other biases. Even when there are enough surveys to produce a mostly reliable average, it’s possible that random chance won’t even out and the average will end up being off. In House elections, there’s also the question of distribution. Even if surveys get the overall vote for the House correct, the distribution of those votes could wind up favoring one party or the other. That could be because of targeting, demographics or some other substantive reason. But it could also simply be luck of the draw. Just as pollsters misread the distribution of Trump’s vote, partly because there were fewer quality state polls than national ones, it’s possible that they’ll misjudge House contests this year because there are few reliable polls in most districts. Good forecasters can extrapolate from national surveys and other districts to project what will happen in under-polled races. But there’s always the chance it won’t work.
Missing the electorate. Both late surges and bad luck are risks to polling in every cycle. What’s especially tricky about 2018 is that so many unusual things are happening at once. Money raised is off the scale. Early voting is off the scale. The president’s unpopularity is off the scale. Trump has actually rallied a bit lately, but at 43.1 percent approval (as calculated by FiveThirtyEight), he still ranks third-lowest of any president in the polling era though 641 days, and his disapproval number is dead last. There’s never been a president who spent virtually all of his first two years having more than half the nation disapprove of him."
So, even if the polls are probably right, there are certainly mechanisms that could throw them off this year. A point to keep in mind.
2. If Trump's popularity is going up, does that make all the polls and forecasts (which are going in the opposite direction) suspect.?
Not really. Trump's modest improvement in his popularity ratings does not, at this point in the cycle, mean all that much. Nate Silver examined this question exhaustively and concluded:
'[W]hile it might seem a bit weird that presidential approval ratings and the generic ballot have moved in opposite directions, the data isn’t that hard to explain. The president’s party usually does poorly at the midterms even with a popular president, and Trump isn’t popular. His numbers are improved, but only marginally. Moreover, the relationship between presidential approval and midterm performance is rough enough that you wouldn’t necessarily expect them to move in lockstep. And Republicans aren’t doing any worse (or better) than you’d expect from historical trends. Maybe the Republican outlook in the House would be even worse without the recent uptick in Trump’s approval rating. But that outlook isn’t good, and while Trump is probably still a net liability for the GOP, Republicans have plenty of problems of their own making too.'
3. So is it really all about turnout?
No, persuasion is still very important. Swing voters are diminished from historical levels but the magnitude of Democratic gains will depend significantly on their ability to reach and convince such voters. David Hopkins points out:
"With Democrats and Republicans both invested in this year's election, a potential nationwide blue wave will require a non-trivial proportion of voters to shift from the GOP (or third parties) in 2016 to Democratic candidates in 2018. There are 25 Republican-held House seats that were carried by Hillary Clinton in 2016, barely more than the minimum net gain (23) needed by the Democrats to take control of the chamber, and it seems unlikely that Democrats could win enough of these seats alone to gain an overall majority. But there are also 16 Republican-held seats that Trump carried with less than 50 percent of the total popular vote, 23 additional Republican seats where Trump received between 50 and 52 percent of the total vote, and another 24 seats where Trump received 53 or 54 percent of the vote. These are the pivotal districts that hold the partisan balance of power in the House. Democrats don't need to peel off a large share of voters who previously preferred Republican candidates in order to capture majority control, but merely energizing their own habitual partisan supporters is probably insufficient to flip enough seats their way absent a modicum of successful persuasion as well."
So there you have it! Keep those cards and letters coming.