Why speaking Spanish matters to presidential hopefuls in Iowa

Latinos in Iowa, overlooked as a political force for years in the state that kicks off the U.S. presidential race, have been getting unprecedented attention in a too-close-to-call Democratic White House nominating fight.

The predominantly white state has seen the Hispanic share of its population more than double to 6.2% since 2000, making it Iowa’s biggest minority group and a crucial voting bloc that could spell the difference in Monday's state caucuses and in the November election.

The population growth has spurred many Democrats seeking the nomination to face President...