I'm not sure this claim can be backed up by data.
Is some support for turnout being a problem. "Wisconsin tells the same numbers story, even more dramatically. Trump got no new votes. He received exactly the same number of votes in America’s Dairyland as Romney did in 2012. Both received 1,409,000 votes. But Clinton again could not spark many Obama voters to turn out for her: she tallied 230,000 votes less than Obama did in 2012. This is how a 200,000-vote victory margin for Obama in the Badger State became a 30,000-vote defeat for Clinton."
My thoughts where people would have been more willing to hold their noses and vote for her if they thought it was going to be a very close election. Few democrats in Michigan really thought the state was up for grabs at something like 78.9% vs 21.1% https://projects.fivethirtyeight.com/2016-election-forecast/...
More support for this is new-hampshire (70-30) was predicted as a closer state than Pennsylvania (77-23), but ended-up very comfortably with Clinton. Remember, Pennsylvania (20) + Wisconsin (10) + Michigan (16) + 227 = 273 and a win.
Now, I am not saying the effect was huge, but in tight elections it does not take much. Further, both the Senate +2 and House +6 shifted toward democrats though maintaining republican leaning.
Many in Clinton’s campaign viewed these voters as Trump’s base, people so committed to the Republican nominee that no amount of visits or messaging could sway them. Clinton made no visits to Wisconsin as the Democratic nominee, and only pushed a late charge in Michigan once internal polling showed the race tightening.
Bill Clinton, advisers said, pushed the campaign early on to focus on these voters, many of whom helped elected him twice to the White House. The former president, a Clinton aide said, would regularly call Robby Mook to talk about strategy and offer advice.
But aides said the Clinton campaign’s top strategists largely ignored the former president, instead focusing on consolidating the base of voters that helped elect President Barack Obama to the White House. In the closing days of the campaign, Clinton targeted young people, Hispanics and African-Americans with laser like focus, casting Trump as a racist who only sought the presidency to benefit himself."
He almost was forced to make his voters believe in an alternative reality in order to actually go out and vote.
If you like or are neutral to candidate X, and dislike Y then voting even if it's pointless still feels good. So, win or lose voting still feels good.
If you dislike X, but dislike Y more then voting feels painful. If you think it's close then you are more willing to go though that pain. But, if you think X will win and you don't want to vote for them then there is little downside to staying home. On the other hand, if you think Y is going to win then you can say to your self it's not a vote for X, it's a vote in protest to Y.
Granted, if you dislike X, and hate Y or have something else you care about, like voting in every election, and are in the booth anyway then that's another story.
Now, this is probably not a huge effect but, in states that where within 1% it still matters.
