Marquette is the best pollster when it comes to Wisconsin, but unless they find Burke with a larger lead or other pollsters (PPP, Quinnipac, SUSA) find Burke up, still tilt/lean R.
Every single poll since April has shown either a 1 point Walker lead, a tie, or 1 point Burke lead. This race is the definition of toss up. To call it "lean R" is completely nonsensical.
It's learn R because the fundamentals favor Walker. Obama is unpopular, it's a midterm, and Democratic turnout will be down. If the race were tied going into election day, he'd be my bet.
