Tariffs are at the center of President Trump’s economic strategy, and since taking office in January, he’s kept them in the spotlight.

He kicked off his second term by imposing them on Canada and Mexico, tying them to border security and illegal drugs. He’s also said imposing tariffs on our trading partners would boost U.S. manufacturing, create “vast wealth” for the country and improve what he perceived as unfair trading relationships that create large annual trade deficits.

Economists warn of a escalating trade war and say his promises on tariffs will be hard to keep.

Part of the reason for that is the unpredictable way he’s rolled out his tariff agenda. He’s frequently changed course, threatening to impose them only to hit pause, shift deadlines or sometimes, double down.

Here’s a look at Trump’s on-again, off-again tariff agenda and how some countries have responded. Note that Trump frequently talks about tariffs in informal settings, but this timeline captures his biggest moves made ahead of Wednesday, which he’s hyped as “Liberation Day” — the day he’ll announce new reciprocal tariffs on a range of U.S. trading partners.