Wealth tax debate rages ahead of US election

Democratic Party contenders ask crucial question

Senators Bernie Sanders and Elizabeth Warren, candidates for the Democratic Party's presidential nomination in the United States, have posed a fundamental question about the role of taxation.

Should it, as they advocate, be used to close the income gap between rich and poor or, as Republicans argue, should tax policy foster economic growth?

How voters in next year's presidential election answer those questions could affect the future of the Democratic and Republican parties－and the US.