As soon as the 45th president of the United States takes office, he will be confronted with a quandary: Where to hold a big fancy party? The White House is old and its rooms are small, which in 2009 led President Obama to host the Indian prime minister, Manmohan Singh, in a temporary pavilion erected on the South Lawn. President Trump will never agree to host a dignitary in such squalor; he’s going to need a ballroom.