At the risk of belaboring the obvious, suppose that Trump had won the popular vote by 2.5 million, but that Clinton had won the Electoral College via narrow wins in several battleground states. This alone would have produced a huge, coordinated national movement, from Republican elites plus mass rallies, demanding that the Electoral College accept the popular verdict. (Such a campaign was actually planned by Rove in 2000, in the event that Bush won the popular vote but lost the electoral vote.)
Then suppose the Clinton campaign had opposed recounts in the close states. At this point, the rhetorical (and possibly actual) violence would have been astounding.
This asymmetry is a puzzling but regular feature of U.S. politics. It's not just about Trump. Imagine the parties in office being reversed when (a) 9/11 happened (especially if the president had brushed off intelligence briefings about the threat), (b) the 2008 financial crisis arose, (c) the economy recovered 2012-2016 (Romney claimed that a smaller recovery would prove his policies were correct), or (d) Benghazi happened (note that not just 9/11 but the 1983 Beirut barracks bombing were far bigger deals, each with highly plausible theories of executive fecklessness in the run-up).