I am trying to maintain perspective on the Trump presidency, but he makes it so hard.

There always is a difference between what presidents say and what they do. In the long run, history focuses on the latter, because actions are more important.

I defy anyone but a deranged history buff to recall one thing that James Garfield or William Taft actually said. Dwight Eisenhower was president for eight years, and all anyone remembers is his farewell speech.

But that does not mean that what presidents say doesn’t matter at all. The president is both the head of government and head of state and, for good or for bad, represents the United States when he (or in the future, she) speaks.

I can still shrug off statements that are patently political or intemperate. Not to totally excuse them because I think it would be better if our president demonstrated patience and courtesy. It is moderately disturbing that the man with the nuclear codes is so easily enraged. Say what you will about Obama — and I could say a bunch — the man managed to appear unruffled even under stress.

Where the line gets totally crossed is when the president appears to use other governmental authorities for political purposes. I was vocal that any use of the IRS during the Obama administration against conservative organizations — remember Lois Lerner? — was plain wrong. Now Trump has made it clear that he wants to use the U.S. Department of Justice for the same purpose.

For those who missed it, Trump recently attacked his own attorney general, Jeff Sessions, and publicly told him what to investigate. Sessions responded with some hostility, and the two are having a public spat.

But here is the problem. Even though the attorney general works for the president, we have always tried to observe some separation so that the prosecutorial powers are, and are seen to be, impartial.

The credibility of the Justice Department depends, in large part, on the perception that investigations and prosecutions are based on objective circumstances and not used for political purposes. (In the interests of full disclosure, I worked at the Justice Department back when dirt was new.)

Now, even if — and it is now a longer shot than it was — Justice decides to investigate any or all of the matters that Trump articulated, there will always be a stench of partisanship. Take for example the firing of former FBI agent Peter Strzok. Based on the known facts, this termination was objectively justified and correct.

Both sides of the political spectrum should agree that you cannot be an effective investigator of the president or of a presidential candidate when you are so clearly partisan and biased. Once Trump, however, turns it into a political football, the entire complexion of the issue changes, and whatever decision is made, it will be suspect.

Lawyers know that words can be powerful. The president should realize that too.

Evan Slavitt is a Massachusetts lawyer who writes on legal issues for the Herald.