A Trump administration appointee is refusing to sign a letter allowing President-elect Joe Biden’s transition team to formally begin its work this week, in another sign the incumbent president has not acknowledged Biden’s victory and could disrupt the transfer of power. The administrator of the General Services Administration, the low-profile agency in charge of federal buildings, has a little-known role when a new president is elected: to sign paperwork officially turning over millions of dollars, as well as giving access to government officials, office space and equipment authorized for the taxpayer-funded transition teams of the winner. It amounts to a...