President Donald Trump’s vow to accelerate construction of a “contiguous, physical wall” along the Mexican border is slamming into a Washington reality – who’s going to pay for it and how? Instead, U.S. taxpayers will foot the bill, starting with money already in the Department of Homeland Security account that amounts to a small down payment. Then it’s up to the Republican-led Congress to come up with $12 billion to $15 billion more, according to an estimate offered by Senate Majority Leader Mitch McConnell, R-Ky., on Thursday from a GOP issues retreat in Philadelphia.