Republicans should be very worried. Not because the GOP might lose the November presidential election, but because it might win.

Donald Trump, the presumptive GOP nominee, has dramatically elevated the threat level behind his potential presidency by suggesting that ethnicity and religion are fair game for choosing a federal judge's qualifications. His remarks came after U.S. District Court Judge Gonzalo Curiel issued a ruling unfavorable to the for-profit Trump University in a lawsuit by former students.

Trump referred to Curiel as a "Mexican" judge who cannot be relied upon to rule impartially because Trump wants to build a border wall. Curiel was born in Indiana and is 100 percent American. His parents reportedly migrated to this country nearly a century ago.

When challenged about who else he might disqualify as biased, Trump stated that Muslims may also be included. Among the president's jobs is nominating federal judges.

Trump appears to be still weighing his options on Jews. Some Trump fans have posted outrageous anti-Semitic messages online, and when asked by CNN anchor Wolf Blitzer whether he condemns such messages, Trump replied, "You'll have to talk to them about that. ... I don't have a message for the fans." But he was quick to denounce the "dishonest" news media for pressing him on this point.

Defenders say Trump cannot be held any more responsible for what his supporters say President Barack Obama was as a presidential candidate, when backers such as Rev. Jeremiah Wright made outrageous public comments. The difference, however, is that Obama condemned it.

Trump refused to apologize for his characterizations of Curiel and instead sought to justify his stance.

Mainstream Republican politicians are now forced into a corner. They can either do what's right for their country by publicly denouncing him and refusing to back his candidacy — as they should — or they can stand sheepishly behind the mathematically certain GOP nominee. Capitol Hill Republicans fear they could lose their congressional seats and hand control to the Democrats if they don't back Trump.

Former Republican House Speaker Newt Gingrich cannot mask his queasiness. He's a Trump supporter touted as recently as last month as a potential running mate. But he denounced the candidate's remarks as "inexcusable" and Trump's "worst mistake" so far.

Others, such as House Speaker Paul Ryan of Wisconsin and Sen. John McCain of Arizona, seem not so willing to stand on personal conviction. In spite of the harsh insult Trump leveled at McCain for the 5.5 years the senator spent being tortured in a Vietnam prisoner-of-war camp, McCain now stands with Trump.

Thinking people cannot escape the conclusion that a Trump presidency would be disastrous for America. If GOP politicians cannot stand for what they know is right, they don't belong in office anymore.

REPRINTED FROM THE ST. LOUIS POST-DISPATCH