Sens. Ted Cruz, R-Texas, and Marco Rubio, R-Florida, who both vied with Trump for the GOP presidential nomination, ripped him for saying federal Judge Gonzalo Curiel's Mexican heritage constituted a conflict of interest in the Trump University lawsuit he is presiding over.
"Of course it's inappropriate to be attacking a federal judge for his race and ethnicity,” Cruz said. “You’ll have to ask Donald to explain why he says the things he does. I'm certainly not going to try to do so."
Rubio said Trump's comments hurt the Republican Party.
"He needs to stop saying it, that man is an American," Rubio said in an interview with ABC Florida affiliate WFTV. "I don't think it reflects well on the Republican Party."
Last week, less than a day after finally throwing his support behind Trump, Ryan distanced himself from Trump's comments about Curiel.
"I completely disagree with the thinking on that," Ryan told a local radio station.
McConnell echoed those sentiments on NBC's "Meet the Press" this weekend, saying, "I don't agree with what [Trump] had to say."
"I think it was a mistake. I hope it was sloppiness," Gingrich said Sunday during an appearance on Fox News.
Another possible Trump running mate, Sen. Bob Corker, said on ABC News' "This Week" that he did not "condone" Trump's comments.
Trump didn't take the criticisms lightly. During a phone interview on "Fox and Friends" this morning, he said that he expected attacks from Clinton on the topic but was "surprised" by Gingrich's remarks.
"As far as Newt is concerned, I was surprised at Newt. I thought it was inappropriate what he said," Trump said.
Returning to Capitol Hill Monday after more than a week in their home states, many Republican senators were reluctant to discuss the latest controversy involving their party's presumptive presidential nominee.
"I am on my way to the office. Thank you," said Sen. Joni Ernst, R-Iowa, when questioned by ABC News at the Capitol.
Sen. Lindsey Graham, R-South Carolina, a frequent critic of Trump's during the primary, said Trump's comments were not appropriate.
Asked if they were racist, Graham replied "I think so," before jumping into a waiting car. Trump has said "I am the least racist person that you have ever met."
Sen. Richard Shelby, R-Alabama, who is supporting Trump as the nominee, disagreed.
"I don't think he is racist at all," Shelby said.
"What if he was German?" he continued, referring to Curiel. "Or what if he was was Polish, or English? Think about it."
ABC's Ali Rogin and Mary Bruce contributed to this report.