The latest poll from Ipsos might be the worst news yet for the federal Liberals in the wake of the SNC-Lavalin affair.

It shows that the party led by Justin Trudeau has the support of just 30 percent of voters, whereas the Conservatives are at 40 percent.

The New Democrats are in third place at 21 percent; the Bloc Québécois is five percent; others had the support of four percent of respondents.

Trudeau's personal approval rating is 40 percent, which is lower than that of Donald Trump in the United States.

The Conservatives were also at 40 percent in an Ipsos poll on March 5, suggesting that the SNC-Lavalin affair is taking a toll on the federal Liberals.

Perhaps most discouraging for Trudeau is that the Liberals are trailing the Conservatives with women and young adults—two groups that supported the Liberals in 2015.

It raises the question whether the prime minister should even lead his party into the next election.

But it won't be that easy for disaffected Liberals to dislodge him.

That's because according to the Liberal Party of Canada constitution, there are only four things that can trigger a leadership contest:

* due to incapacity, Trudeau ceases to be recognized by the Governor-General as the party leader in the House of Commons;

* the leader dies;

* the leader is not endorsed in a leadership endorsement ballot at or prior to the first national convention after a general election;

* or the national board of the party declares that the results of a leadership vote are invalid.

The party executive can't pass a resolution to dump him.

So if Trudeau doesn't voluntarily resign, he will likely be leading the Liberals into the next general election on October 21.

The only possible exception would be for the Liberal caucus to vest its confidence in another person to be the prime minister. This could conceivably lead the Governor General to rule that Trudeau has an "incapacity" to remain as party leader in the House of Commons.