President Donald Trump is concerned that his Supreme Court darling Justice Neil Gorsuch — whose appointment is regularly cited by the White House as a top accomplishment under Trump — is too liberal, The Washington Post reported.

According to administration officials who heard about Trump’s complaints and spoke with the Post, Trump was frustrated by Gorsuch’s recent vote against the administration on an immigration case, which reportedly pushed him to question whether Gorsuch was going to be a reliable conservative voter on the high court. Another Trump adviser who spoke with the Post said Trump was just complaining about that specific case, not Gorsuch’s dependability overall.

Earlier this week, Gorsuch sided with the four liberal Supreme Court justices — and was the deciding vote — in a case focused on Attorney General Jeff Sessions and the Trump’s administration’s efforts to deport immigrants who have committed crimes. Gorsuch and the four liberal justices ruled that a provision in the Immigration and Naturalization Act that calls for the deportation of undocumented and legal immigrants who have committed violent crimes was unconstitutionally vague because it doesn’t properly define what a violent crime is

While he reportedly grumbled about Gorsuch in private, in public, Trump responded by passing the buck to Congress in a tweet.