Sen. Cory Booker is getting a jump on the 2020 presidential contest by lodging unusually stiff opposition to a fellow senator nominated for President-elect Trump's cabinet.

The New Jersey Democrat is planning to testify against the confirmation of Sen. Jeff Sessions, R-Ala., to serve as attorney general.

The unprecedented move is a sure-fire way to energize the Democratic base. The party, demoralized and frustrated since November, is hungry for bold leadership willing to take the fight to Trump and Republicans in Congress.

Sen. Tom Cotton, R-Ark., who harbors ambitions of his own and also is known to occasionally buck convention, called it a "disgraceful breach of custom."

"I'm very disappointed that Senator Booker has chosen to start his 2020 presidential campaign by testifying against Senator Sessions," Cotton said in a Facebook post. "This hearing simply offers a platform for his presidential aspirations. Senator Booker is better than that, and he knows better."

It's smart politics for Booker, 47, the former mayor of Newark with ambitions for higher office.

"It's pretty interesting to watch his attempts to raise his profile in recent weeks. He clearly wants to have a bigger role in the political process," said Jim Manley, a Democratic operative who previously advised his party's leadership in the Senate.

In brief comments to the Washington Examiner on Tuesday, Booker sidestepped questions about his political motives. He said that his opposition to Sessions was about the Republican's record as a public official.

"This is about the issues," Booker said. "This is about the next attorney general, the highest law enforcement officer in the country."

In previous generations, it was rare for senators to oppose the nomination of fellow senators to administration posts.

Even eight years ago, in an already politically charged atmosphere, Democrat Hillary Clinton, then a New York senator, was confirmed for secretary of state with 94 votes. Only two Republicans voted against her.

Democrat Ken Salazar, then a Colorado senator, won unanimous confirmation to serve as interior secretary.

So in a chamber that has traditionally prided itself on comity and decorum, Booker's decision to go beyond voting against Sessions on the Senate floor, and testify against him at his confirmation hearing in the Judiciary Committee, is drawing notice.

With Clinton's loss to Trump and President Obama's exit from the White House, Democrats are desperately in need of fresh leadership.

Booker aims to deliver, framing his opposition to Sessions as a disagreement over federal voting rights. The issue is important across the Democratic Party, but especially to African Americans, an influential group inside the progressive base.

Booker upending Senate tradition to testify on this issue not only satisfies progressives' desire to fight Trump, it could raise his profile among the kind of liberal activists that can sway Democratic presidential primaries.

It might also help Booker avoid resistance to any presidential bid he might launch in four years from Democratic activists that are suspicious of the New Jerseyan's ties to Wall Street.

"Cory Booker's testimony against a fellow senator is an early sign that Democrats are going to fight back against Trump from Day One," said Ed Espinoza, a Democratic operative in Austin, Texas. "It could also be an early sign that Booker is testing the 2020 waters."

Booker delivered an impassioned speech at the Democratic convention in Philadelphia last July.

The address wasn't flawless — Booker didn't lay down the sort of marker for the future that Obama did in 2004, when he addressed the Democratic convention in Boston when he was just a Senate candidate.

But Booker left Democratic activists talking about his future, and further established himself as a rising star inside the Democratic Party. Karen Finney, a veteran of Clinton's 2016 presidential campaign, said Booker also left a good impression through his effective work on behalf of the nominee.

"He is certainly someone who is widely respected, so I think certainly he does have a platform," Finney, a Democratic political operative, said.