The Senate confirmed Omaha attorney Brian Buescher last week to be U.S. District Court judge for Nebraska. Not a single Democrat voted for him, despite his obvious qualifications.

And we know why.

Democratic Sens. Mazie Hirono of Hawaii and Kamala Harris of California sought to undermine his confirmation by arguing Buescher's Roman Catholic faith made him unfit for the job. Their chief point of contention: that Buescher is a member of a shadowy, extremist group known as — the Knights of Columbus.

Sadly, Hirono’s and Harris’ bigoted insinuations are not outliers. Their opposition to Buescher's nomination continues a trend of Senate Democrats suggesting Catholics ought to be excluded from holding public office.

Sen. Dianne Feinstein of California, for example, told Judge Amy Coney Barrett in 2017 that the “dogma lives loudly within you,” suggesting the then-nominee was just too Catholic to be a federal judge. Sixteen years earlier, Feinstein and Sens. Dick Durbin of Illinois, and Chuck Schumer of New York, winked and nodded at Judge William Pryor’s Catholic faith, questioning his "deeply held beliefs."

This should alarm the 2020 Democratic primary candidates as they seek to convince the country they represent all Americans.

Anti-Catholic bias is nothing new in the United States, and it is no secret that the ultra-liberal and exceptionally pro-choice fringes in the Democratic Party harbor a deep hatred for the teachings of the Catholic Church.

What is new is that top Democratic lawmakers have adopted a similar disliking for practicing Catholics, and they have no problem whatsoever expressing it publicly. It used to be that this bigotry was whispered and on the peripheries. But now, the bigotry is out in the open, as top Democrats feel emboldened to express openly their deep disdain for the largest religious denomination in the country.

It was bad enough when they opposed it quietly. It is worse that they are doing it openly.

The 2020 Democratic primary candidates, especially the openly religious ones, need to speak out on this. Reporters need to press them on it.

The primary candidates need to show that there are still adults in the Democratic Party and show voters that the senators who have attempted to impose religious litmus tests on Catholic nominees are the minority.

There are a number of 2020 candidate who can do this.

Former Vice President Joe Biden, for example, is a Roman Catholic who claims his faith has played a significant role in his personal and professional life. Will Biden stand up to members of his own party and defend his faith?

What about the other self-professed Roman Catholic candidates, including Sen. Kirsten Gillibrand of New York and former Reps. John Delaney of Maryland and Beto O’Rourke of Texas? What about former Secretary of Housing and Urban Development Julián Castro, who claims the “Catholic faith has never been far" from his life?

What about South Bend, Indiana, Mayor Pete Buttigieg, who attends an Episcopal church and makes faith a major component of his professional life? What about Sen. Amy Klobuchar of Minnesota, a congregationalist who is also married to a Roman Catholic?

Surely, at least one of these candidates will stand up for Catholics against the bigotry of Senate Democrats. If not, then the Democratic Party really is as lost as it seems.