Nearly 2 in 3 Americans think the nation’s economy is in good shape, and most of them believe President’s Trump’s policies are at least somewhat responsible for that. More Republicans rate the economy positively than do Democrats. As Congressional primaries continue and Americans look ahead six months to their midterm votes, Mr. Trump looks like a positive factor among Republicans, 7 in 10 of whom say they’d prefer a candidate he backs — but the president’s influence is limited to his own party. More Independents say they’re less likely to support a candidate backed by Mr. Trump. Meanwhile on the...