Who could replace Trudeau as Canadian prime minister, with Trump threatening tariffs?

Canada's Justin Trudeau announced his resignation as prime minister Monday, with his Liberal Party in turmoil amid declining poll numbers and an election on the horizon. 

Whoever assumes leadership in the unpopular governing party will become the next prime minister, and that person must tackle rising costs of living, an immigration crisis and aggressive economic pressure from President-elect Trump – not to mention the challenge from Canada's ascendant Conservative Party in the next election, to be held no later than October. 

The next Liberal Party leader will be chosen in a national leadership contest, according to the Canadian Broadcasting Corporation. Party President Sachit Mehra said Monday he would call a meeting "to be held this week to begin the nationwide democratic process of selecting a new leader of the party."