Though the African-American senator co-sponsored the "killer legislation", it was eventually rejected.

The Clinton campaign had been more vocal on the issue saying that she was voted in its favour and was not "lukewarm" in her response as Democrats are perceived on the issue.

"She looked into the issue.... She decided to vote in favour of the nuclear deal and was a supporter of it," Clinton campaign chairman Terry McAuliffe said.

However, the strongest backing for the stalled deal has come from Obama's Republican rival John McCain who said the nuclear agreement will strengthen ties with the world's biggest democracy and involve India in the fight against nuclear proliferation.