A record 47% want stronger unions. Labor's challenge is turning support into power.

For only the second time in a quarter century, a majority of Republicans — 52% — approve of labor unions, according to a new Gallup poll. Why it matters: Despite Americans' rising approval, union membership remains near a modern low. Congress has repeatedly blocked labor's biggest priorities, and House Republicans are now investigating unions, even as their own voters approve of them. Republicans' warmer feelings toward unions don't translate into wanting them to wield more power: 49% of…