Rep. Ken Buck (R-CO) announced Thursday that he will not support an impeachment measure against Homeland Security Secretary Alejandro Mayorkas, putting the measure of impeachment at risk of not having enough votes to pass.

The impeachment measure against Mayorkas is being pursued by House Republicans over the secretary’s handling of the southern border. Buck, who previously said that he was undecided on whether he would support impeaching Mayorkas, explained that he would not support such a measure because Mayorkas’s handling of the border is “a policy difference,” not a “high crime.”