Democrats clearly need Biden, but equally clearly: They do not want him. Intent to the point of hell-bent, Democrats are looking to run to the left and away from the moderates they will need to win. This threatens to make them weaker than they were when they lost to Trump in 2016, at the same time he promises to be stronger than he was then.

According to RealClearPolitics’ latest average of national polling on the Democrat contenders, Biden is below where he was before the debates began. Although his drop from 32 to 30.5 percent is slight, the fact he is not gaining — despite being the Democrats’ only consequential establishment option — is significant.

Even more significant is the collective Left’s continued gain. Prior to the first debate, the left of the Democrats’ field (everyone except Biden, Bullock, Delaney, and the since-withdrawn Hickenlooper) stood at 55 percent; now it is at 58.5 percent.

Because most are following the Democrats’ contest like a horse race, they miss the contest’s real dynamic. The race is not Biden against another candidate — regardless of who it is. It is Biden versus “the field” — and the Democrats’ field is clearly the Left. The problem for Democrats is that Biden is not closing, while “the field” is gaining, and the clock is running.

To put the Democrats’ 2020 leftward tilt into perspective, compare it to 2016’s results. In that two-person race, Clinton was the establishment and she won 54.8 percent of awarded delegates; Sanders was the Left and he won 45.2 percent. Today’s Left is well ahead of where Clinton was, and Biden is well behind where Sanders was. All current evidence also suggests that as today’s race continues, the Left will rise even more.

Looking back demonstrates the danger ahead for Democrats.

According to 2016 exit polling, liberals comprised just 26 percent of voters, while conservatives were 35 percent and moderates 39 percent. Clearly, neither a liberal nor a conservative can win without moderates, but liberals need substantially more.

To attain 50 percent of the electorate, liberals must almost double their own percentage. Obtaining the additional 24 percent of the electorate means they must win 61.5 percent of moderates. In contrast, at 35 percent, conservatives need only an additional 15 percent — equating to just 38 percent of moderates.

Liberals are playing on a field decidedly tilted against them. How hard this makes it for 2020 Democrats, bent on nominating a Left candidate, is also shown by 2016 exit polling. Clinton won 52 percent of moderates then; Trump, just 40 percent.

Comparing then to now, with a 2020 nominee of the Left, Democrats will need significantly more moderates than Clinton won — despite Hillary being closer to them on the ideological spectrum than their 2020 nominee will be. And Hillary still lost in 2016, even while dominating among moderates to a greater degree than the Democrats’ 2020 nominee will.

Contrastingly, with full support of conservatives (he won only 81 percent in 2016) in 2020, Trump’s 2016 moderate support is above the amount he would need in 2020 — and running against a Left Democrat will make him more likely to attract moderates.

Biden remains the biggest threat to Trump, but he remains the Democrats’ unlikely nominee. On their increasingly leftward course, Democrats will be hard-pressed to match Clinton’s 2016 showing. At the same time, with incumbency and the economy, Trump is quite likely to increase his 2016 results.

In short, Democrats will need moderates more in 2020 than they did in 2016, but are likely to get fewer moderates in 2020 than they did in 2016. In contrast, Trump may need moderates less in 2016 than he did in 2020, but is likely to get more moderates in 2020 than he did in 2016.

Democrats could not be more dependent on this key voter segment. Yet the candidate who could help them most with moderates is the one they are least likely to nominate. As in any race, there is a price to be paid for betting with your heart instead of your head. Right now, Democrats appear insistent on paying it.

J.T. Young served under President George W. Bush as the director of communications in the Office of Management and Budget and as deputy assistant secretary in legislative affairs for tax and budget at the Treasury Department. He served as a congressional staffer from 1987 through 2000.