BRUSSELS—Thursday’s summit of European Union leaders will elevate to the highest political level a fight over a new Russian natural-gas pipeline that is supported by Germany but strongly opposed by the U.S., which fears could further undermine Ukraine’s financial and political stability. The dispute over the planned expansion of OAO Gazprom’s Nord Stream pipeline, dubbed Nord Stream 2, has been simmering below the surface for months, especially since German Economy Minister Sigmar Gabriel promised to protect the project from “political meddling.” The talks will put the bloc’s commitment to easing Moscow’s grip over its eastern members and neighbors to a test. German Chancellor Angela Merkel will likely be pressed to voice her views on the pipeline. “We want to be heard and we hope this message will be taken on, especially by the chancellor,” a Slovak diplomat said Wednesday. Slovakia is one of seven Central and Eastern European states […]