In June, after a terrorist attack in London, Isaac reposted and commented on a CNN International story that quoted a Catholic bishop saying "This isn't in the name of God, this isn't what the Muslim faith asks people to do."
Isaacs responded: "CNN, Bishop if you read the Quran you will know 'this' is exactly what the Muslim faith instructs the faithful to do."
Isaacs was announced Thursday as the Trump administration's pick to become director general of the United Nations' International Organization for Migration, or IOM. The 169-member organization has a nearly $1 billion annual operating budget and for decades has deferred to the United States, one of its top benefactors, to lead the organization.
Trump's pick could be at risk of being the first U.S. nominee since the late 1960s to lose an election by the group's voting members, according to several people involved in international relief coordination.
"I don't know the nominee, but I've seen some of his statements and they reflect a troubling prejudice that is really incompatible with a position of leadership for the world's most important international migration agency," said Eric Schwartz, president of Refugees International and a former assistant secretary of state under President Barack Obama.
"The person who leads this needs to be a symbol of the international community's support for humanity. And that means that dark-skin people and Muslim people have the same inherent worth as any other people."
Isaacs was in Bangladesh on Thursday, providing diphtheria treatment to Rohingya refugees, when his nomination was announced.
After The Post sent a sampling of his social media activity to the State Department, along with a request for comment, his Twitter account was made private, and the department provided a statement from Isaacs apologizing for his posts.
"I deeply regret that my comments on social media have caused hurt and have undermined my professional record," his statement read. "It was careless and it has caused concern among those who have expressed faith in my ability to effectively lead IOM. I pledge to hold myself to the highest standards of humanity, human dignity and equality if chosen to lead IOM."
In a separate statement, spokeswoman Heather Nauert at the State Department said the agency would continue to support the nomination and stressed that Isaacs has a proven record of helping diverse populations around the globe.
"Mr. Isaacs has apologized for the comments he posted on his private social media account. We believe that was proper for him to do so. Mr. Isaacs is committed to helping refugees and has a long history of assisting those who are suffering. We believe that if chosen to lead IOM, he would treat people fairly and with the dignity and respect they deserve."
Isaacs's public media posts caught the department by surprise and were not reviewed before his announced nomination, State Department officials familiar with the matter said.
During the administration of President George W. Bush, Isaacs served as the U.S. Agency for International Development's director of foreign disaster assistance. The agency led U.S. relief efforts after the 2004 Indian Ocean tsunami and a massive earthquake in Pakistan in 2005.
As a vice president at Samaritan's Purse, an organization led by the Rev. Franklin Graham, son of the evangelist Billy Graham, Isaacs has in the years since coordinated the group's international relief efforts. In 2014, Isaacs was an outspoken advocate for the United States and Europe to lend more aid to Sierra Leone, Guinea and Liberia to stop the spread of a deadly outbreak of Ebola.
In 2015, Isaacs visited a mostly Syrian refugee camp in Greece, writing in a post on Facebook that "On multiple occasions I wiped tears away listening to their stories. I was happy for them and glad to be a part of meeting their needs and showing them the unconditional love of Christ as we help them in five countries."
But in that same post, Isaacs expressed more controversial views, going on to pen what he called an "evening rant." Isaacs ridiculed Obama for wanting to accept large numbers of Syrian refugees as a "foolish and delusional" attempt to "show cultural enlightenment."
Isaacs wrote that he had spent two hours in the refugee camp and that his visit had been long enough to conclude that there were dangers lurking in the groups of refugees.
"I know what a fighter looks like, how they carry themselves, how they group, and how there is tension in the air around them. Clearly the non-Syrian camp was 75% single males and while many rural refugees were there; there were also many men who have known violence," Isaacs wrote. "I feel most of the refugees are fine people but there are real security risks and this can't be swept under the rug."
In other social-media posts, Isaacs divided refugees along religious lines and said Christians in at least one instance should receive preferential treatment.
In a series of tweets criticizing Obama's position on Syrian refugee relief in the fall of 2015, Isaacs wrote: "Refugees are 2 grps. Some may go back and some can't return. Christians can never return. They must be 1st priority."
Later that day, Isaacs wrote in another tweet: "If Islam is a religion of peace, let's see 2 million Muslims in National Mall marching against jihad & stand for America! I haven't seen it!"
Ibrahim Hooper, national communications director for the Council on American-Islamic Relations, a frequent critic of the Trump administration, said that "this type of nomination coming from the Trump administration is a symptom of its deep hostility toward immigrants, migrants and Muslims."
Hooper said Isaacs's professed views should be disqualifying: "It is imperative these positions maintain neutrality with regard to religion, national origin and . . . frankly have some sympathy for those who are migrating for no choice of their own but the economic and social pressures they are under."
The election to lead the IOM is scheduled for June. A nominee must receive the support of two-thirds of its voting members.
Isaacs's views on climate change and dwindling natural resources, factors the United Nations has cited increasingly as contributing to international migration, may also cause consternation abroad. Writing on Facebook in reference to the Paris climate accord in 2015, Isaacs called a connection between national security and climate change "a joke."
"The meeting in Paris next week is not going to be a rebuke to ISIS. It is going to be a dinner joke, a laughing stock, and a diversion of all the real issues."
In an undated radio interview with the Christian radio program "First Person" with Wayne Shepherd, audio of which is available online, Isaacs said he sees young people as overly focused on social justice.
"I guess I'm an older guy, but I see rights as coming from God and not from governments. And any time that a government gives a right — let's say that it was decreed by law that everybody has a right to clean water, everybody has a right to a house — who's going to pay for that?" Isaacs said.
"It doesn't matter what it says on paper, what matters is what people are expected and allowed to do based on the rights given to them by God. You know, sadly, clean water's not a human right. It is something we all want to aspire to see people to get, but it's not a right, it's not guaranteed anywhere, and you have to work for it."
In 2010, the U.N. General Assembly explicitly recognized a human right to water and sanitation, calling the two "essential to the realisation of all human rights."
Maria Sacchetti contributed to this report.