WASHINGTON — A senior administration official started the day giving an Iran peace plan a 75% shot but upped the odds to 85% by Friday afternoon — as the White House sought to calm concerns that President Trump could sign a bad deal. “I’m calling 75% confidence that we’re going to be signing this agreement soon,” the senior official told reporters in a small-group morning call around 10 a.m. on the heels of Trump’s Thursday afternoon announcement that the plan was “approved” by Iranian leaders.