Tulare, Calif.

It’s 105 degrees as I stand with Rep. Devin Nunes on his family’s dairy farm. Mr. Nunes has been feeling even more heat in Washington, where as chairman of the House Select Committee on Intelligence he has labored to unearth the truth about the Federal Bureau of Investigation’s activities during and after the 2016 presidential campaign. Thanks in large part to his work, we now know that the FBI used informants against Donald Trump’s campaign, that it obtained surveillance warrants based on opposition research...