The Senate’s top Democrats insisted in a letter to President Trump on Monday that any deal with North Korea must completely dismantle Pyongyang’s nuclear and ballistic missile programs permanently — and that the White House must loop Congress in on its plans before negotiations begin. The minority leader and several ranking Democrats issued a list of conditions in anticipation of the expected June 12 summit between Trump and Kim Jong Un, pressing the president to maintain a tough and unsparing stance with the North Korean leader and with his ally China to ensure that the talks achieve the goal of...