For much of the summer, the political intrigue on the presidential campaign trail centered on Donald Trump and whether he was serious about running for president. Now, the early August chatter is all about Joe Biden mounting a possible challenge to Hillary Clinton for the Democratic nomination. Josh Robin filed the following report.

They've known each other for years and briefly ran against each other in 2008. Now, in the twilight of both of their careers, Hillary Clinton may once again face Joe Biden. And outwardly at least, the president says it's all up to his vice president.

"There is no denying that Vice President Biden has been a terrific vice president, but ultimately, he has his own personal decision to make about whether or not he wants to run for the presidency of the United States," said White House Press Secretary Josh Earnest.

It's a run that may be inspired by the death of Biden's son in May at age 46. As he neared the end, Beau Biden reportedly encouraged his father to do it, arguing that the White House should not "revert to the Clintons."

Word that Biden was strongly considering stepped on the release of Hillary Clinton's first television ads in early primary states.

Clinton tops polls, but increasingly, voters don't trust her.

She had no public events Monday. On CNN Sunday, Clinton Communications Director Jennifer Palmieri said, "I have a great deal of love for Vice President Biden, a lot of respect, and so do the Clintons, everyone on the campaign, and we're going to let him make his decision."

But that decision isn't just about whether Biden wants it. It's also about whether it's not too late. The election is 15 months away. That may seem like a lot of time, but winning requires money and staff, both of which have gone to Clinton.

David Axelrod, an architect of the Obama-Biden wins, advised the vice president to sit out.

"I'd hate to see him risk it all on a campaign that likely wouldn't succeed," Axelrod said on NBC's "Today."

Biden ran in 1988 and 2008.

He also didn't speak publicly Monday. His office said, "As the Biden family continues to go through this difficult time, the Vice President is focused on his family and immersed in his work. In recent weeks, the Vice President has worked on the nuclear deal with Iran, traveled across the country to highlight the Administration's economic priorities, and more."

There is no word yet on whether that "more" will include another race for the White House.