President Donald Trump said Sunday that he won't back down on his sweeping tariffs on imports from most of the world unless countries even out their trade with the U.S., digging in on his plans to implement the taxes that have sent financial markets reeling. Speaking to reporters aboard Air Force One, Trump said he didn't want global markets to fall, but also that he wasn't concerned about the massive sell-off either, adding, "sometimes you have to take medicine to fix something.” His comments came as global financial markets appeared on track to continue sharp declines on Monday, and after Trump's aides sought to soothe market concerns by saying more than 50 nations had reached out about launching negotiations to lift the tariffs. The higher rates are set to be collected beginning Wednesday, ushering in a new era of economic uncertainty with no clear end in sight. Trump’s tariff blitz, announced April 2, fulfilled a key campaign promise as he acted without Congress to redraw the rules of global trade. It was a move decades in the making for Trump, who has long denounced foreign trade deals as unfair to the U.S and is gambling that voters will be willing to endure higher prices for everyday items to enact his economic vision. Countries are scrambling to figure out how to respond to the tariffs, with China and others retaliating quickly. During his chat with the journalists, Trump also commented on TikTok. The president on Friday said he was signing an executive order to keep TikTok running in the U.S. for another 75 days to give his administration more time to broker a deal to bring the social media platform under American ownership. Beijing hit the brakes on a deal on Thursday after Trump announced wide-ranging tariffs around the globe, including against China.