WASHINGTON—Joe Biden’s emergence as the 2020 Democratic presidential front-runner is widely cast as a victory for moderates over progressives. But the former vice president’s platform also shows how far left the party’s center on economic policy has moved in recent years.

On taxes, health care, climate change and labor rights, Mr. Biden proposes a significantly bigger government role than Hillary Clinton did during her 2016 presidential bid and what the Obama-Biden ticket advocated during their two White House campaigns.

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