"I believe the United States is going to regain its leadership position in the international community. We've got a great candidate, Joe Biden, to do that," Inslee, a Democrat who dropped his own White House bid last year, said in an interview with CNN's Christiane Amanpour after he had made his endorsement in an earlier statement.

Gore said in a tweet that he's "proud" to endorse Biden, the presumptive Democratic presidential nominee, and appeared later in the day with him at a virtual Earth Day event.

The endorsements come as the US continues to grapple with the health and economic impacts of the coronavirus pandemic , which has killed more than 46,000 Americans and brought the country's economy to a standstill as businesses shutter to avoid spreading the illness.

Inslee said he believes Biden could help restore the economy as president.

"Earth Day is a day to celebrate the potential of restarting our international economy by building a clean energy economy that can put millions of people to work, cause massive reinvestment, which our economy is going to need so desperately as we come out of this pandemic."

The governor also lauded Biden's previous work on environmental issues, noting that he had "introduced the first bill on climate change in the United States Senate" when he was a senator from Delaware.

Inslee, whose presidential campaign focused heavily on the climate crisis, had criticized Biden's climate plan during the CNN Democratic debate in August, seemingly insinuating that the former vice president didn't understand the issue's urgency.

"The time is up, our house is on fire," he said at the time.

Gore, who is a leading voices on environmental issues, said during his event with Biden that voters who care about the climate crisis have an easy choice when it comes to Biden and President Donald Trump.

"If there is anyone out there who has any doubt whatsoever about the choice to be made in this election, it is simple. It is not complicated. It is clear cut," he said. "Vote for Joe Biden. Vote against Donald Trump. Put us on the road to solving the climate crisis and creating a brighter future."