The Trump White House has repeatedly sounded an alarm about visitors with ties to China’s Communist Party coming to the United States, arguing that they are a potential security threat. But the administration appears to have literally left the door open to a member of a Chinese government group when it went along with a plan to give the biggest purchasers of President Trump’s digital currency access to the president and the White House. Mr. Trump launched a so-called memecoin, a type of cryptocurrency, just days before his inauguration. To bolster sales, the president’s business partners created a contest in April, offering the coin’s top buyers a tour of the White House and a private dinner with Mr. Trump at his Virginia golf club. One of those buyers was He Tianying, who is a member of the Chinese People’s Political Consultative Conference, according to government documents in China examined by The New York Times.