This is a much-needed post, as far as it goes. The media shifted from projecting internment for the Republican party to reading the last rites over Democrats with whiplash speed. Reality lies nowhere near either of those poles.
The President-elect clearly takes office with no mandate, as you explain. The Republican party as a whole has a slightly better case, having narrowly held the Senate against steep odds and winning the “national” vote for the House by about 3 million, but the argument is marginal at best. The Democrat party clearly had a bad cycle, with Secretary Clinton failing to defeat a very flawed candidate and significantly underperforming President Obama’s two wins essentially across the board, while Democrats all but whiffed in Congress and in State races.
A fair reading may be that both parties lost, with the Democrats having lost a little worse. Voter turnout dropped sharply. Accusations of Republican suppression don’t come close to explaining this. Third party candidates ran stronger than usual, though they did not have the breakout cycle that might have been expected given the high negatives of the major party candidates. An explicit None of the Above alternative for the Presidential ballot might have polled quite well.
The core problem is that neither party has a mandate, and the same would have been true had Secretary Clinton won PA, WI, and MI by the same squeaker margins. True mandates are not often entirely personal in nature (with President Obama as a possible exception). They are the melding of the right message and a messenger to embody it. This is true on both sides, the clearest cases of the 20th Century being FDR and Ronald Reagan. In 2016, neither party had a message — it was an election about nothing. The President-elect ran a steadfastly issue-free campaign, but Secretary Clinton was little better. She had position papers on many issues, but never brought them front and center in the campaign. She ran as not-Trump.
The issues were out there for both parties. The national debt is climbing to unprecedented levels; entitlements are swallowing the budget; climate change continues unabated (and will continue even in the unlikely event that the Paris Agreement gains traction in the real world); economic growth has been meager for 16 years, despite epic stimulus efforts; and America’s standing in the world is at its lowest ebb since the post-Vietnam years. These represent decidedly bipartisan failures. Each party blames the other and, for once, they’re both right.
A President will take office with a mandate when a candidate grabs two or three issues, runs on them (persuading rather than evading), and wins convincingly. That is a meaningful win. Until it happens, no one will have a mandate.