The U.S. presidential election in November is the most consequential in modern history. Whether the increasingly authoritarian, vindictive and dangerous President Donald Trump wins another four years in power could define the United States for a long time to come.

This year's election will be no typical struggle between two parties that differ more in degree than in kind. But first, the Democrats must select their candidate, and this time that contest is exceptionally fluid.

Former Vice President Joe Biden's third attempt to win the country's top job isn't going much better than the first two. Biden is a well-liked figure — a decent, empathetic man who lacks a mean streak. But Biden's very likability might well be his electoral undoing. He lacks what I call presidentialness — a certain dignity and remoteness that conveys the sense that crossing him or her would be unwise. He also lacks a message: reminding Democrats that he was Barack Obama's vice president tells voters little about how he would govern.