How has US culture become so coarse, so quickly?

I subscribe to an email list from the White House “1600 Daily”. I periodically receive news alerts and “what is going on” messages from the Administration. At 9:01 am eastern on 7/20/17 I received an email that said:

Yesterday, I met with Republican Senators at the White House and told them that now is the time for action. Obamacare was a big lie. “You can keep your doctor”—lie. “You can keep your plan”—lie. Now, people are hurting, and inaction is not an option. We must repeal and replace this disaster. The Senate should not leave for summer recess until it has passed a plan to give our people great healthcare. I’m ready to act; I have pen in hand. I’ll sign the legislation into law, and then we can celebrate for the American people.

– President Donald J. Trump

“You can keep your doctor”, “You can keep your plan” are statements made by President Obama. It is not too much of a stretch to say President Trump is calling President Obama a liar.

Ronald Reagan was campaigning for election in 1984. At a visit to Portland Oregon he was greeted by protesters. During Reagan’s speech a man shouted “Liar, liar, pants on fire!” We were shocked that anyone would show the lack of civility to interrupt a President and call him a liar.

My question is not whether or not Presidents or politicians lie, but rather: What has happen in our culture when our President is able to call a previous President a liar in an “official” (I presume) White House communication?

We were appalled 33 years ago when a citizen called the President a liar. When our sitting President calls a previous President a liar, the action seems par for the course. How has US culture become so coarse, so quickly?