For consumers who want to support the U.S. economy, determining a product's homegrown credentials is no easy task in today's global economy — but it's an important question amid a new era of import tariffs and ongoing renegotiations of long-standing trade pacts. Few origin stories are as complicated as that of a modern automobile, whose badge and even assembly location don't tell the whole story. Enter Cars.com's American-Made Index, which ranks the most American models on the market. Which cars top the list for 2018?