This week, the typically upbeat, jovial Joe Biden sounded anything but during a speech in Washington.

"President Obama and I have been very quiet and respectful, giving the [Trump] administration time," the former vice president said Thursday night. "But some of these roots are being sunk too deeply. I believe it's time to challenge some of the dangerous assumptions."

Biden went on to excoriate the Trump administration's foreign policy. While accepting an award from Center for Strategic and International Studies, Biden said he was worried the country is "walking down a very dark path that isolates the United States on the world stage."

The sober and stark speech was just one of several public appearances Biden made over the past week, including a campaign appearance in Alabama with Doug Jones, the Democrat running in the state's special Senate election.

And in November, Biden is set to release a new book, which means the veteran politician who somewhat regretfully passed on a 2016 bid will make many of the same media stops that Democratic presidential candidate Hillary Clinton did when she promoted her recent campaign memoir.

All these moves raise the question of what, exactly, Biden is trying to accomplish — a possible political comeback or simply being protective of the policies he and former President Barack Obama helped implement.

Biden specialized in foreign policy during his lengthy Senate career and was a key player in many of the Obama administration initiatives that Trump is now trying to undo — the Paris climate accord, the Trans-Pacific Partnership and, possibly next, the Iran nuclear deal.

"We're seeing a shift toward a theory of foreign policy that is closed-off and clannish," Biden said Thursday. "One that groups the world into 'us' and 'them.' "

It's clear Biden is deeply offended by — and worried about — Trump's international approach.

"Among the many problems plaguing this administration's foreign policy: ideological incoherence. Inconsistent and confusing messaging," the former vice president said. "Erratic decision making. Unwillingness or inability to solve problems caused by understaffing."

But that doesn't explain the political events like the Jones rally in Alabama and comments by his daughter that her father hasn't ruled out another White House run just yet.

Democratic political strategist Steve Schale was involved in the "Draft Biden" effort ahead of the 2016 presidential race but doesn't think Biden's rising profile should necessarily be viewed through a 2020 lens.

"He has been very active trying to help win support for state parties and down ballot candidates his entire career," Schale said. "He said when he left office he was not going to stop. He engaged in a Delaware state Senate race, he was just involved in Florida state Senate race. I think whether or not Joe Biden decides he wants to enter the 2020 conversation or not, the fact that he is out doing what he's done his entire career shouldn't come as any surprise to anybody."

Nonetheless, Schale was quick to embrace the sales pitch that might accompany a third Biden run.

"I think it's quite possible that for the perfect response to Trump is somebody like Joe Biden, who is older, experience, very competent, very trustworthy," the Democratic strategist said. "I think it could be a really nice contrast."

But "older" and "experienced" aren't necessarily positives to some Democrats right now. Many ultimately viewed Hillary Clinton's decades-long career in the national spotlight as a major liability. Biden had already been in the Senate for 20 years when Clinton became first lady in 1993.

Still, it's clear Biden loves the public eye, and at the Alabama rally, he had the crowd laughing and clapping along as Biden impersonated senators he served with and regaled them with his well-worn Scranton, Pa., stories.

"Every time someone would lose a job, my dad would repeat — if we heard it once, we heard it 50 times — 'Joey, remember, a job's about a lot more than a paycheck. It's about your dignity. It's about your respect in the community,' " Biden said at the rally for Jones.

He is also trying to draw contrasts with the populist, nationalist message Trump rode to victory, and Democrats have long called upon Biden, with his blue-collar roots, to help them in more rural areas. As the midterms approach and those are places Democrats need to win in order to make inroads in the House and protect Senate seats, he will likely be a natural, in-demand surrogate once again.

"The appeal to populism and nationalism is a siren song," Biden said during his D.C. speech on Thursday. "A way for charlatans to aggrandize their power, raise themselves up, break down those mechanisms designed within our Constitution and internationally to limit abuse of power, and destabilize the world."

Still, one of the problems Biden is sure to run up against is that the party is in search of new blood, and some in the party aren't so eager to look backward.

"I think that it's time to pass the torch to a new generation," Rep. Linda Sanchez, D-Calif., said this week, referring to the septuagenarians that lead the Democrats in the House. "They are all of the same generation. And again, their contributions to the Congress and to the caucus and the conference are substantial. But I think there comes a time when you need to pass that torch, and I think it's time."

But it's clear Biden isn't ready to move out of the spotlight just yet, which appears to be as much about protecting what he and Obama built together as it is keeping his own political options open.

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