President-elect Donald J. Trump announced on Sunday that he would name Massad Boulos, a Lebanese American businessman and the father-in-law of his daughter Tiffany, as a senior adviser covering Arab and Middle Eastern affairs.

It was the second time this weekend that Mr. Trump offered a position in his administration to an in-law, coming one day after he tapped Charles Kushner, his daughter Ivanka’s father-in-law, to serve as ambassador to France.

In an announcement that did not mention the family connection, Mr. Trump praised Mr. Boulos’s business experience and his contributions to his presidential campaign.

“Massad is an accomplished lawyer and a highly respected leader in the business world, with extensive experience on the International scene,” Mr. Trump said on social media. “He has been a longtime proponent of Republican and Conservative values, an asset to my Campaign, and was instrumental in building tremendous new coalitions with the Arab American Community.”

Before the election last month, Mr. Boulos played a major unofficial role in the Trump campaign, courting Arab American voters who Republican strategists hoped would support Mr. Trump out of frustration with President Biden’s support for Israel. Despite Mr. Trump’s own defiantly pro-Israel policies during his first term as president, Mr. Boulos worked to build support for him in heavily Arab American and Muslim corners of Michigan.

Through his connection to the Trump family, Mr. Boulos has already served as something of an informal liaison between Mr. Trump and Middle Eastern leaders. In September, Mr. Boulos met with Mahmoud Abbas, the leader of the Palestinian Authority, on the sidelines of the United Nations General Assembly in New York. He also helped deliver a letter from Mr. Abbas to Mr. Trump in July, in which Mr. Abbas wished Mr. Trump well after an attempted assassination that month.

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