The user shared a Breitbart article headlined: "President Donald J. Trump has backed the fight to save the critically ill British baby Charlie Gard..."
The Mean Girls actress replied to the tweet, saying: "THIS IS our president. Stop #bullying him & start trusting him. Thank you personally for supporting #THEUSA."
She later replied to another tweet saying the Trump family "are kind people". "As an American, why speak poorly of anyone?" she added.
Trump supporters praised the London-based actress for her tweets.
Others, however, were not so pleased with her comments.
Lohan has given mixed signals regarding her political allegiance. In February, she said: "He is the president - we have to join him. If you can't beat him, join him."
However, during the election campaign, she tweeted Hillary Clinton saying "I couldn't understand you more". After Trump's victory she tweeted "Retweet if you want a recount", a message she later deleted.
Lohan's warm words for the president could be considered surprising after crude comments Trump made about her in 2004 resurfaced during the election campaign.
In an interview on The Howard Stern Show, Trump asked the shock jock what he thought of the former child star.
"I think she's hot," Stern replied.
"There's something there, right?," Trump said. "But you have to like freckles. I've seen a, you know, close up of her chest and a lot of freckles. Are you into freckles?"
Stern said he was not, before asking Trump if he could imagine "having sex" with Lohan.
"She's probably deeply troubled and therefore great in bed," Trump said.
"How come the deeply troubled women, you know, deeply, deeply troubled, they're always the best in bed?"
A representative for Lohan criticised the comments at the time, Rolling Stone reported. "Donald Trump is a perfect example that money cannot buy you class. As a man, I am disgusted."
