Rahul Gandhi, the scion of India's most fabled political dynasty, will within weeks be crowned leader of the Congress party, handing him a freer rein to prove if he can mount a credible challenge to the dominance of Prime Minister Narendra Modi.

The great-grandson of India's founding prime minister, Jawaharlal Nehru, has struggled to convince voters — and many in his party — that he is leadership material, especially after a drubbing in the 2014 general election.

Modi's depiction of the 47-year-old as an undeserving "prince" has helped sideline Gandhi since the last national vote, during which time Congress has suffered some of its worst-ever local election results.