The constitutional threshold for impeaching Cabinet members should be lower than for the President, the Vice-President, and federal judges. Let me explain.
Impeaching federal judges threatens judicial independence. As a result, long-settled practice is that they should not be impeached for their opinions. You usually need actual crimes.
Impeaching the President or Vice President threatens democracy in a sense. They are the only ones elected by something approximating the nation. (Yes, Andrew Johnson is a more complicated example because he was not elected President, but set that aside for now.) Congress is, of course, also elected, but maybe only the voters should get to decide the President/VP’s fate absent clear crimes like Watergate.
Cabinet officials, on the other hand, are neither independent nor elected. They are also easily replaced. The main argument against impeaching them on policy grounds (as opposed to, say, felonies) is that they were implementing executive policy. Impeaching them will not change policy. Only impeaching the President can do that. But that’s unclear. The impeachment, removal, and disqualification of a Cabinet officer may make it difficult for the President to find someone else willing to commit the same high crimes and misdemeanors.
Does that mean any current Cabinet members should be impeached? I don’t know–let’s see the evidence.