Michelle Wu called on her top challenger Josh Kraft to release his tax returns to reveal any financial interests or business “entanglements” he may have with the city that could impede his ability

Boston Mayor Michelle Wu is leading Josh Kraft by 30 points with about a month to go before the first ballots are cast in the city's preliminary election.

The poll of 500 Boston voters likely to participate in the Sept. 9 preliminary election showed a wide gulf between Wu and Kraft, who drew 30 percent support to her 60 percent.