Former Massachusetts Gov. Bill Weld, a Republican taking on President Trump in 2020, challenged his fellow GOP members to watch the president's rally in North Carolina and ask if that is the party they "signed up for."

During Trump's Wednesday night rally, the president's comments over Rep. Ilhan Omar (D-Minn.), one of the four minority congresswomen he recently told to "go back" where they came from, prompted the crowd into chants of "send her back."

"I challenge every Republican to watch @realDonaldTrump's rally last night, complete with chants of 'Send her back,' and ask if that is the Party of Lincoln and Reagan we signed up for," Weld tweeted Thursday morning. "We are in a fight for the soul of the GOP, and silence is not an option."

The long-shot candidate is the only Republican to officially mount a primary campaign against the president in 2020.

Earlier this week, former South Carolina Rep. Mark Sanford (R) said he is considering a possible candidacy.

And Rep. Justin Amash (I-Mich.), who recently left the Republican Party after vocally opposing Trump, said he wouldn't rule out a run.

Trump's rally followed a week of backlash against the president's Sunday tweet targeting Reps. Omar, Alexandria Ocasio-Cortez (D-N.Y.), Ayanna Pressley (D-Mass.) and Rashida Tlaib (D-Mich.), telling them to "go back" to where they came from.

All four are women of color and U.S. citizens, and only Omar, who came to the U.S. at age 12 as a refugee from Somalia, was born outside the United States.

The House voted to condemn Trump for his "racist" tweets on Tuesday. Just four Republicans, Reps. Susan Brooks (Ind.), Brian Fitzpatrick (Pa.), Will Hurd (Texas) and Fred Upton (Mich.), voted with every Democrat to condemn the tweets.