Following his father's attacks on the Congresswoman over her remarks on the 9/11 terror attacks, he shared several critical quotes.
One retweet from Donald Trump supporter Will Chamberlain, called Ms Omar - who is a US citizen but came to America as a child refugee from Somalia - "a walking advertisement for more restrictive immigration and refugee policies".
"Nothing about her public statements indicates that she has any meaningful allegiance to this country or its people," it added. "Her politics are sectarian, not American."
Mr Trump also accused people reporting death threats against Ms Omar of "telling one side of the story", while sharing numerous critical tweets.
While speaking on Islamophobia, had said “CAIR was founded after 9/11 because they recognised that some people did something and that all of us were starting to lose access to our civil liberties.”
The American political right quickly weaponised her wording and the president shared a video of the speech cut with 9/11 footage.
Ms Omar said she would "defend democracy" as criticism continued on Saturday.
"This country was founded on the ideas of justice, of liberty, of the pursuit of happiness. But these core beliefs are under threat," she wrote on Twitter.
"No one person – no matter how corrupt, inept, or vicious – can threaten my unwavering love for America. I stand undeterred to continue fighting for equal opportunity in our pursuit of happiness for all Americans."