HERE’S A safe rule for presidential appointments: If a nominee feels compelled to shut down or veil his social media accounts soon after being named, there’s an excellent chance he lacks the judgment for the job and should withdraw.

Exhibit A for the rule — call it the Bonehead Bar — is Ken Isaacs, nominated as the Trump administration’s choice to lead the United Nations’ International Organization for Migration (IOM), which spends $1 billion annually to aid migrants worldwide. Within days of his nomination, The Post’s Aaron C. Davis and Jack Gillum reported that Mr. Isaacs peppered his Twitter account with ignorant, prejudiced and incendiary comments.

The report immediately prompted Mr. Isaacs’s Twitter account to go dark, and he quickly issued the sort of ritual apology we have come to expect when bigotry is exposed. He characterized his social media posts as “careless” and said he would hold himself “to the highest standards” as head of the U.N. agency.

That’s nice to hear. Unfortunately for Mr. Isaacs, it may be too late. While the director generalship of the IOM is traditionally reserved for an American, in deference to the substantial contribution the United States makes to its budget, the nominee, who would serve a five-year term, remains subject to an election by the agency’s voting members. And Mr. Isaacs’s venomous views are unlikely to endear him to an international body whose core mission depends on compassion and tolerance.

They include the frequently debunked idea that Islam is an inherently violent faith; that Christians should be accorded priority in fleeing violence and war; and that he is able to distinguish fighters from bona fide refugees by the “tension in the air around them.” He also dismissed as a “joke” the idea that climate change and national security are connected — a link that scholars, security experts and members of both parties in Congress have made for some time.

Mr. Isaacs is not without relevant experience. He is an executive at an international relief organization called Samaritan’s Purse and served in the George W. Bush administration as director of foreign disaster assistance for the U.S. Agency for International Development. However, his risible views are in line with the Trump administration’s general hostility to Muslim refugees and immigrants. That makes him a poor fit for the job to which he is nominated.

His unsuitability is all the more apparent given the contrast with the man he would succeed at the helm of IOM: William Lacy Swing, a deeply respected and experienced diplomat who served as U.S. ambassador in six postings — to South Africa; Nigeria; Liberia; Congo; the former People’s Republic of the Congo (now Congo Republic); and Haiti. That a public servant of Mr. Swing’s stature would be succeeded by someone who holds views as narrow-minded as those expressed by Mr. Isaacs would be not only a blow to a U.N. agency whose mission is critical at a time of huge migrant flows across the globe. It would also be an embarrassment to the United States.

Read more here: