Barack Obama has acknowledged he has considered running for US president in 2008, despite earlier claims he would serve as senator until 2010.
Barack Obama is two years into his six-year Senate term
"Given the responses I've been getting... I have thought about the possibility," the Democrat said on NBC.
Mr Obama, currently the US's only black senator, said he would give the matter more thought after the mid-term vote.
He was recently on the cover of Time magazine, with the headline Why Barack Obama could be the Next President.
Mr Obama burst onto the national scene with a widely-acclaimed speech at the Democratic Party's convention in Boston in July 2004.
Now, two years into his first term as senator for Illinois, he has dismissed suggestions that he might lack the experience necessary for the White House.
"I am not sure anyone is ready to be president before they are president," the 45-year-old told NBC's Meet the Press programme on Sunday.
Mr Obama had said after his 2004 election, and again earlier this year, that he would serve his full six-year term in the Senate.
"That was how I was thinking at that time," he said.
Adding: "After 7 November [mid-term elections]... I'll sit down and consider, and if at some point I change my mind, I will make a public announcement and everybody will be able to go at me."