Will Elon Musk Austin-ify Brownsville? Some folks in Texas's poorest city see a new downtown mural funded by the billionaire's foundation as the writing on the wall.

Organizations such as Voces Unidas RGV, a pro-immigration and community-development group that has a sizable Facebook following, have added SpaceX to the hot-button issues—the border wall, pipeline projects, reform of U.S. Immigration and Customs Enforcement—they organize for and against.

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