Republican Sen. Susan Collins of Maine is taking GOP presidential candidate Donald Trump to task for his remarks about a federal judge.

NBC

Trump attacked Judge Gonzalo Curiel after he ordered the release of documents in a lawsuit targeting Trump University. Trump said he didn't think Curiel could be unbiased because of his Mexican heritage. Trump wants to build a wall to keep out illegal immigrants from Mexico.

Collins said Trump's comments on the heritage of judges was "absolutely unacceptable" and showed a lack of respect for the principle of separation of powers.

Collins said back in May that she could support Trump if he stopped the "gratuitous personal insults" and "bizarre" behavior.