When Prime Minister Justin Trudeau unveiled his cabinet Wednesday, there was a notable absence: no appointment for a government leader in the Senate.

One constitutional law professor says that’s a significant change that signals a new direction, but could also present challenges for the new Liberal government.

“It certainly indicates that he’s going to stick to his plan of not having any senators in his caucus,” University of Ottawa professor Carissima Mathen told CTV’s Canada AM Thursday.

In early 2014, Trudeau removed all Liberal-appointed senators from his caucus in what he called a first step toward reforming the scandal-plagued Red Chamber.

During the election campaign, Trudeau pledged to appoint senators through a non-partisan, “merit-based” process.

Not appointing a government leader in the Senate seems to be the first step towards that promise. But many questions remain about how the Senate will function with a Conservative majority and a group of senators who are Liberals, but not in the Liberal caucus, Mathen said.

The biggest question, she said, is: “How will this Conservative-dominated Senate deal with Liberal legislation?”

It’s unclear how Trudeau plans to deliver on his Senate reform promises. 

There are currently 47 Conservative senators and 29 senators who used to be in the Liberal caucus, but are now technically independent. There are 22 vacancies in the Senate. 

Traditionally, senators are appointed directly by the prime minister, and along party lines. 

But if Trudeau makes any Senate appointments, he has indicated that an independent panel would assess potential candidates and make recommendations, Mathen said.

However, any final decisions would still be Trudeau’s, she said.

“The choice does remain his because under the Constitution, the prime minister must retain ultimate control for appointing senators.”

Sen. David Smith, who was appointed by former Liberal prime minister Jean Chretien, said he believes the Senate can function as a non-partisan chamber of “sober second thought.”

At a recent Senate meeting, “the mood was as non-partisan as I’ve ever seen it,” he told CTV News Channel Thursday.

With a “comfortable majority,” the Conservatives could theoretically “torpedo everything” in the Senate, Smith said.

But he doesn’t believe that will happen. 

“There was no mood of that at all,” he said.

Since Trudeau removed them from caucus, Liberal senators now consider themselves “independent Liberals,” who can vote freely, Smith said.

“We are not whipped. We can vote with our conscience and what we think makes sense.”