WASHINGTON — Members of the Trump administration on Monday fanned across cable news stations and in front of crowds of loyal supporters to make the case for Donald Trump’s latest tariffs on Canada as the president himself moved to escalate the trade war.

Trump posted on social media that he intends to double tariffs on Canadian automobiles and auto parts to 50 per cent on Jan. 1. Later in the day he escalated that further, threatening to shut off the pipes which carry natural gas and oil from Western Canada to Ontario and Quebec via the United States.

“Canada will be treated like a State no longer! On Trade, and in other ways, also, they are among the worst Nations in the World to deal with,” Trump said in the first post. “They feel entitled, and yet, WE DON’T NEED CANADA, THEY NEED US!”

Trade talks between Canada and the U.S. fell apart Friday, triggering 50 per cent tariffs on a host of Canadian goods.

The move to hit one of America’s largest trading partners with more duties could prove challenging for Republicans ahead of November’s midterm election who are already staring down increased gas and consumer prices amid the closure of the Strait of Hormuz.

The Canadian tariffs could play an significant role in deciding which party holds the majority in the Senate. They’re unlikely to be popular in states where close races are expected including Maine and Michigan.

Trump’s trade czar earlier Monday tried to downplay the impact of the duties and blamed Canada for the unsuccessful trade talks.

United States Trade Representative Jamieson Greer told CNBC the new duties cover about five per cent of Canadian imports, saying it’s “a pretty low amount in the grand scheme of things.”

Greer accused Canada of wanting more from the Trump administration in “the last hours.” He dismissed reports that Commerce Secretary Howard Lutnick had inserted himself in the negotiations and was unhappy with the deal.

“Simply, they wanted more. I don’t know if it was political for them. It certainly doesn’t make economic sense,” Greer said. “But perhaps for political reasons, they have some byelections coming up. I don’t know, but they came in and they wanted, they want more, and we weren’t prepared to do that.”

Prime Minister Mark Carney on Saturday accused the U.S. of trying to introduce the last-minute measures, including restrictions on Canada’s ability to do deals with other countries.

Carney promised to retaliate with dollar-for-dollar tariffs by Sept. 8.

American and Canadian sources have pointed to tariffs on heavy trucks as a major point of contention. Canada expected exemptions or reductions on the duties and Trump officials were unwilling to budge.