Donald Trump. AP Photo/John Locher Real-estate tycoon Donald Trump was watching the so-called GOP undercard debate Tuesday and did not seem to be a fan of two of the candidates in particular.

The Republican presidential front-runner repeatedly tweeted and retweeted messages critical of Sen. Lindsey Graham (R-South Carolina) and former New York Gov. George Pataki (R).

Both Graham and Pataki used their lower-tier debate opportunity to rip into Trump's plan to temporarily bar Muslims from entering the US.

Trump responded on Twitter, sharing messages saying Pataki needs a "brain surgeon" and that Graham is "weak," among other insults.

See some of Trump's responses below: