A stronger argument is that no president should use the power of his office to try to dig up dirt on a political opponent — as, for instance, Lyndon Johnson did, abusively and persistently, to Barry Goldwater in 1964. That’s absolutely true.
But disgraceful behavior is not the same thing as criminal behavior. Democrats may now find themselves in the curious position trying to convince the country that Trump should be booted from the office to which he was lawfully elected for behavior that, whatever else might be said about it, was not unlawful. That will be a tough sell.
No wonder Trump seems to be spoiling for this fight. With an eye on Bill Clinton’s presidency, he may even relish a lengthy impeachment battle that uncovers no crime while showing that congressional Democrats are more intent on pursuing a vendetta against a president than helping the people they’re elected to serve.