With President Donald Trump's so-called “Liberation Day” of tariff implementation fast approaching, Senate Democrats are putting Republican support for some of those plans to the test by forcing a vote to nullify the emergency declaration that underpins the tariffs on Canada. Republicans have watched with some unease as the president's attempts to remake global trade have sent the stock market downward, but they have so far stood by Trump's on-again-off-again threats to levy taxes on imported goods.