Utah’s Sen. Mike Lee, a champion of the Constitution’s separation of powers and the prerogatives of the U.S. Senate, has been presented with a golden opportunity to put his vote where his mouth is.

He should stand firmly against the nomination of Ron Mortensen to head the State Department bureau that deals with migrants and refugees.

Utah’s other senator, the soon-to-retire Orrin Hatch, is so far in the tank for the current occupant of the Oval Office that he might not be reachable on this matter. Though his public doubt about the administration’s new wave of tariffs suggests reason for hope.

The nomination of Mortensen creates problems — for Lee and for the country — on so many levels. Enough that Lee has the duty — and, quite possibly, clout — to block it.

Before being nominated as Assistant Secretary of State for Population, Refugees, and Migration, Mortensen’s claim to fame was as a particularly hostile blogger and pundit whose broken record was a hostility to illegal immigration and an overly dim view of the millions of human beings who now live among us as productive and peaceful neighbors.

It would be fair for the administration and its allies to note that Mortensen’s hostility has been focused on those who have come here without official authorization. But the theme of his screeds is a bigoted view that such humans can be freely categorized as criminals.

He wrote that the Obama administration’s Deferred Action for Childhood Arrivals “rewards illegal aliens (the so-called ‘Dreamers’) for destroying the futures of innocent American children.“ He accused Sen. John McCain of wanting to roll out “the welcome mat for ISIS on America’s southern border.”

His view of undocumented migrants is that “people illegally in the United States routinely commit multiple felonies and other serious violations of American law when they enter the country.”

Mortensen, of course, has the constitutionally protected right to hold and express such views. His concerns about identity theft and misuse of other people’s Social Security numbers are not pointless and should be better addressed by Congress and the administration.

But, surely, somewhere in our nation, somewhere in the deep catacombs of Foggy Bottom, there is a person who is better qualified to run this office. Someone who can do the job with fidelity to the law, with concern for American citizens and legal residents, but without a history of thumping the tub for this nation to turn its back on its core values of sanctuary and relief in the name of a frankly paranoid strain of xenophobia.

Someone who can take the rough edges off the president’s worst instincts, not further enable them.

Lee and Hatch might also be concerned that, in choosing to nominate a Utahn without first consulting the senators from that state, the administration has committed a serious faux pas of constitutional courtesy.

Sen. Jeff Flake, R-Ariz., has already come out against Mortensen’s confirmation and, with the Senate so closely divided, it will only take a few more Republican defections to block it.

Utahns Hatch and Lee could, and should, tip the balance.