Dr. Jill Biden had been thought to oppose a 2016 run, but on Sunday her spokesman didn't dispute an NBC News report that she is "not an obstacle" to a Joe Biden bid for the Democratic nomination.

"Of course Dr. Biden would be on board if her husband decides to run for president but they haven't made that decision yet," Jill Biden spokesman James Gleeson said in a statement.

Joe Biden is still weighing a 2016 bid -- which would involve taking on Hillary Clinton's high-powered campaign and the insurgent Vermont Sen. Bernie Sanders -- in the wake of the death of Biden's son, Delaware Attorney General Beau Biden.

The vice president has said he is still trying to determine whether he is emotionally prepared to fully commit to what would be his third presidential campaign. His first two came in 1988 and 2008.

A group of nearly 50 top Democratic Party fundraisers and activists are circulating a letter urging Biden to jump into the Democratic White House race, saying he is sure to win if he does.

"The Obama-Biden administration has been a spectacular success. But much work remains to be done," the letter said. "To finish the job, America needs a leader who is respected both home and abroad, and who understands the real challenges facing American families."

Signatories to the letter, first reported by Reuters, include former South Carolina Democratic Party chairman Dick Harpootlian, and John Maa, who serves on the party's national finance committee as well as retired basketball legend and coach Elgin Baylor.

An outside group of supporters of the vice president called Draft Biden 2016 has been preparing the groundwork for a potential Biden run, including setting up infrastructure in key states.

One of the big impediments to a late run by the vice president would be whether he could swiftly raise sufficient campaign funds to be competitive in early state nominating races which start in February -- a factor the donor letter, signed by 48 potential donors and supporters, appears intended to address.

CNN's Stephen Collinson contributed to this report