There are some things a rat won’t do. Character is defined by choices, and particularly by choices under very difficult circumstances.

A new mandate is going out from the National Institute of Health. From now on, lawyers will be substituted for rats in all laboratory experiments. There are three reasons for this decision.

Before I tell it, I apologize to lawyers. The hero at the end of this piece is a lawyer.

Two recent events — John McCain’s decision to effectively endorse Donald Trump, and Paul Ryan’s “ disavowing ” Trump’s racist comments but supporting him anyway — called to my mind one of my favorite jokes.

If ever there were a moment when the nation, and particularly the GOP, could use some major demonstrations of character, it’s now.

If ever there were a moment when the nation, and particularly the GOP, could use some major demonstrations of character, it’s now. And instead, it seems like its party leaders are getting bested by the rats.

Sen. McCain was shot down, injured and imprisoned by the North Vietnamese. He was tortured, and he suffered. And then he came home and successfully managed a long career in public service. Now he’s almost 80 years old.

Wouldn’t this have been the moment for him to risk re-election in order to stand up to Trump, a man who publicly humiliated McCain and questioned his service? A man who declared, “I like people who weren’t captured.” The comment demeaned not only McCain, but also all who ever risked — or gave — their lives for our country. Wouldn’t this have been the perfect occasion for McCain to say, “On behalf of all who have served, fought and sacrificed for the United States, I will not now or ever endorse Donald Trump!”

Sen. John McCain, R-Ariz., pictured on June 3, 2016. (Wong Maye-E/AP)

Just when we needed him to be brave, John McCain lost his nerve. He could have helped the country remember its better self. Instead, he debased himself and surrendered his dignity, and for what? What could the senator still want out of politics that is more valuable than his honor and the honor of the Armed Services?

And then there’s Paul Ryan. The House speaker “disavowed” Trump’s racist remarks about Hispanic and Muslim judges, but declared that he backed the candidate anyway. You cannot back a racist candidate without supporting his racism. That’s not just disingenuous, it’s impossible.

Think for a moment about political courage as we’ve seen it at important moments in our country. Think about William Lloyd Garrison, Martin Luther King, Harriet Tubman, Rosa Parks, Elizabeth Cady Stanton, Margaret Sanger.