WASHINGTON, DC, USA (AP) — No votes have been cast in the Democratic presidential nominating contest, but the winnowing has begun.

A distinct top tier of candidates is breaking away from the pack in early polling and fund-raising, building distance between themselves and the rest of the bloated field. Although the first nomination contest in Iowa is still more than six months away, tighter qualifying standards for the fall debates and cash flow problems have prompted questions about how many campaigns will still be operational next year.

Five candidates have pulled away from the pack: former Vice-President Joe Biden, Vermont Senator Bernie Sanders, Massachusetts Senator Elizabeth Warren, California Senator Kamala Harris and Pete Buttigieg, the mayor of South Bend, Indiana. Biden has consistently led early polls, with the four others jostling for position behind him. Most other candidates have struggled to even hit two per cent in recent surveys.

Money has also flowed disproportionately to the top five candidates. Buttigieg, who led the field in second quarter fund-raising with $24.8 million, raised more than a quartet of senators — Amy Klobuchar, Cory Booker, Kirsten Gillibrand and Michael Bennet — combined.

“There’s a field of likelies, unlikelies and possibles,” said Sue Dvorsky, the former chairwoman of the Iowa Democratic Party.

Even as the primary field cleaves into haves and have- nots, big questions remain about what direction the party will take as voters weigh who best, and how best, to defeat President Donald Trump next year. The top tier includes moderates and liberals; the oldest contender in the race and the youngest; and a black candidate.

At this early phase, the enduring strength of the leading White House hopefuls is unclear. Biden is a fragile front-runner, whose decades-long political career will continue to be picked apart. Harris faces questions about whether she can sustain her spurts of dynamism. Buttigieg is struggling with black voters, the backbone of the Democratic Party. And some Democrats anxiously wonder whether Sanders and Warren, the most liberal candidates in the race, could win a general election.

“This fall is when voters get serious,” said Jim Demers, a Booker supporter who chaired Barack Obama’s 2008 campaign in New Hampshire. “That’s when we’re going to know who’s real and who’s not.”

Each of the top-tier candidates appears certain to still be in the mix when voters start taking a more serious look at the race. But that’s far from a sure thing for some White House hopefuls mired at the bottom of the pack.

Former Colorado Governor John Hickenlooper’s fund-raising has largely dried up, and he has less than $1 million in the bank. Ohio Rep Tim Ryan raised just $899,000 in the second quarter, far from what is needed to fund a campaign apparatus in the early voting states.

Other lower-tier candidates are still building out operations aimed at sustaining them through a long campaign.