On November 9, 2016, President Obama told the nation, "No matter what happens, the sun will rise in the morning and America will still be the greatest nation on earth". He immediately invited Donald and Melania Trump to the White House, and spent hours briefing his successor, who had never held elected office, on things he didn't know (appointments to be made, etc).
On January 20, 2017, Barack and Michelle Greeted Donald and Melania at the door of the White House with warmth and grace. As is custom, President Obama gave President Trump a grace period, after which he criticized his policies and performance, as is the right of every citizen, former President or not.
In 2000, the state of Florida - and the election - was divided by less than 600 votes (out of 5 1/2 million in Florida and more than 100 million nationwide). Gore legally challenged the election. It went to the Supreme Court, it was decided. Al Gore went on television and said "I called Governor Bush, and congratulated him on his victory. [Smiling] Then I promised I wouldn't call him back".
Every President of my lifetime (I'm 55) has proudly carried on the tradition which Reagan spoke about so eloquently in 1981.
Until now, I've never heard talk about militia taking to the streets if The President loses, or seen a President so petty as to refuse to hang his predecessor's picture in The White House.
Like it says in the song, "You don't know what you got 'til it's gone".