And on Twitter, June 14th is #JohnMcCainDay -- a clear dig at the President on his favorite social networking platform

Thousands of users decided to troll the President on his 73rd birthday on Friday by celebrating his late Republican rival John McCain . By mid-morning, the hashtag #JohnMcCainDay was a top Twitter trend.

It all started with Andy Lassner, the executive producer of "The Ellen DeGeneres Show."

Honoring an American hero today. Let's celebrate @realDonaldTrump 's birthday today by having #JohnMcCainDay trend. I'm sure this would mean a lot to patriot like Donald Trump. #JohnMcCainDay

"Honoring an American hero today," Lassner wrote. "Let's celebrate @realDonaldTrump's birthday today by having #JohnMcCainDay trend. I'm sure this would mean a lot to [a] patriot like Donald Trump."

Users responded to Lassner's callout and the hashtag quickly went viral -- it even reached the top of the trending list on Twitter.

Pretty soon, even members of Congress were joining in -- though it's not clear they were aware how it started.

"It is your character, and your character alone, that will make your life happy or unhappy." - John McCain



A good day to remember the example of Senator McCain indeed. #JohnMcCainDay pic.twitter.com/ilyW2j1vHE — Rep. Marc Veasey (@RepVeasey) June 14, 2019

Democrats Rep. Joyce Beatty tweeted a McCain quote -- "Be brave -- the rest is easy," and Rep. Marc Veasey did too, saying it was "a good day to remember the example of Senator McCain indeed."

Political advocacy groups joined as well.

We had a lot of policy disagreements with John McCain and battles over use of military force. We never held back in our fights. But, we also always honored his sacrifice and heroism, in uniform. We still do. And that's what we're honoring, on this #JohnMcCainDay pic.twitter.com/oCEaf7uiXI — VoteVets (@votevets) June 14, 2019

"We had a lot of policy disagreements with John McCain and battles over use of military force. We never held back in our fights. But, we also always honored his sacrifice and heroism, in uniform. We still do. And that's what we're honoring, on this #JohnMcCainDay," VoteVets, a liberal political action committee, wrote.

But not everyone found it funny, with critics from the right and left.

"Sooo... the same people who call Donald Trump 'petty' and 'childish' are busy trying to rebrand his birthday #JohnMcCainDay today... got it," conservative political comedian Tim Young wrote.

Sooo... the same people who call Donald Trump "petty" and "childish" are busy trying to rebrand his birthday #JohnMcCainDay today... got it. — Tim Young (@TimRunsHisMouth) June 14, 2019

Others felt it was unfair to McCain himself.

"I support a #JohnMcCainDay. We should have one for the sacrifices this man made for our nation," Carmine Sabia wrote. "But to do it on President Donald Trump's birthday is petty and disrespectful to the senator. You are not doing it to honor him. It should be on August 29. Stop using him for narrative."

I support a #JohnMcCainDay. We should have one for the sacrifices this man made for our nation. But to do it on President Donald Trump's birthday is petty and disrespectful to the senator. You are not doing it to honor him. It should be on August 29. Stop using him for narrative. — Carmine Sabia (@CarmineSabia) June 14, 2019

Trump has not responded publicly to the #JohnMcCainDay campaign.