At the same time Hillary Clinton has become the presumptive Democrat presidential nominee in the race to the White House, a new book claims there's no such thing as systematic gender bias in US politics.

The provocative argument has been put forward by political scientists Jennifer L. Lawless and Danny Hayes in Women on the Run, published last month.

They argue that women campaigning for Congress do so under exactly the same conditions men and that, instead of caring whether a candidates' DNA contains a Y chromosome, it is the party they are aligned to that counts to voters and political elites.

Women are just as successful campaigners, just as good at raising funds and just as talented at winning races, they claim - and they have data to prove it.