President Donald Trump doubled tariffs on foreign-made steel and aluminum to 50%.In a proclamation Tuesday, the White House said the tariffs would end "unfair trade practices" and threats that would "impair national security," while encouraging American companies to invest in domestic plants. "He's delivering on his promises to bolster our steel and aluminum industries in this country and to protect jobs," White House Press Secretary Karoline Leavitt said.But some economists warn that the tariffs could spike prices, impacting cars, auto parts, grocery packaging like canned foods, and construction and transportation building materials.According to government data, steel prices are up 16% since Trump took office, costing more than double what they do in China and one-third more than in Europe per metric ton. The U.K. is also temporarily exempted from the higher tariffs after reaching an initial, separate trade agreement with the U.S.Some industry experts also warn that the new tariffs are only part of a larger solution needed to boost American manufacturing. While the president's tariffs may be helpful, they say a consistent trade policy is necessary.While he fights challenges to his other tariffs in court, Trump is using his executive power through a different, more well-established trade policy on specific industries. The tariffs on aluminum and steel build on a Commerce Department investigation from his first term, which determined that foreign aluminum and steel were a threat to national security. Meanwhile, the president is being sued for his more wide-ranging tariffs, where he broadly claims most countries are treating the U.S. unfairly on trade.