Frustrated by the lack of progress on a signature issue from his 2016 election campaign, Trump unexpectedly told Mexico last week to take a harder line on illegal immigration or face 5 per cent tariffs on all its exports to the United States starting on Monday, rising to as much as 25 per cent later in the year.

Republicans are deeply concerned that Trump’s proposed 5 per cent tariffs on all imports from Mexico would spike U.S. consumers’ costs, harm the economy and imperil a major pending US-Mexico-Canada trade deal.

The border crossing comes after U.S. President Donald Trump threatened to slap tariffs on Mexican imports unless Mexico does more to stop the passage of migrants through its territory.