While the political and media worlds have obsessed about Ukraine and the House effort to impeach President Trump, Joe Biden has been rapidly losing his grip on the Democratic presidential race. In fact, he has already lost it; at least in the national contest, Biden is a front-runner no longer.

Back in May of this year, Biden had an enormous 26.8 percentage point lead over the second-place Democrat, Sen. Bernie Sanders, in the RealClearPolitics average of national polls. By late June, that lead had shrunk to 15.6 points. By Sept. 1, it was 13.5 points. By mid-September, it was 9.7 points.

Now, Biden's lead is 2.2 points, which is essentially no lead at all. He is just ahead of Sen. Elizabeth Warren, with Sanders having fallen farther back and the rest of the field in the mid-to-low single digits.

Certainly Biden has not been helped by Trump, locked in an impeachment battle with House Democrats, characterizing Biden and son Hunter Biden as corrupt. "Look, Biden and his son are stone-cold crooked," the president said at the White House Wednesday. Even if the public knows virtually nothing about the Bidens' case, it's not good to be called corrupt 24/7.

That could account for a decline in Biden's support in the last week or so. But Biden's numbers have been trending downward for months.

The reasons are not hard to find. First, Biden has run a low-energy, uninspiring campaign, while Warren has made a much better effort. Second, and most important, Biden is too old to be president.

What are the chances that Biden will suddenly become a high-energy, inspiring campaigner? About the same as the chances he will become younger.

In the first months of the campaign, the weakness of Biden's "restoration" theme was that it reminded voters that he is a figure from the past. Discussing senatorial colleagues from 40 years ago just added to the impression that he is an old man.

For the record, Biden will be 78 on Inauguration Day 2021 — older than Ronald Reagan was when he left office after serving eight years. Biden would turn 80 in his second year in office. If he were to serve two terms, Biden would be president until age 86. That is totally uncharted territory in American politics.

Recently President Jimmy Carter, who is now 95, said, "If I were just 80 years old, if I was 15 years younger, I don't believe I could undertake the duties I experienced when I was president. You had to be very flexible with your mind."

Carter was 52 when he became president.

Biden's age might also attract increased attention because of Sanders' recent health problem. Sanders is one year older than Biden — they were by far the two oldest front-runners in any presidential race, ever. Sanders was hospitalized Tuesday with chest pains; doctors inserted two stents to open a blocked artery. It is not clear whether Sanders suffered a heart attack.

No, Biden did not have a health crisis of his own (although many took notice when he appeared to have minor bleeding in the eye during an early September debate). And of course anyone, including a younger candidate, could have a problem. But Sanders' heart situation only served to remind voters of the risk of an older candidate.

Of course, Warren is not exactly young — she will be 71 on Inauguration Day. But voters seem comfortable with the idea of a septuagenarian president — in the 2016 election, electing either Trump and Hillary Clinton assured a president in his or her 70s.

And, despite a few missteps, Warren is running a vigorous, sharp campaign. No one has whispered that she has lost a step, or just isn't as quick or as able as she used to be.

This week Biden struck back for the first time against Trump's "stone-cold crooked" attacks. "Let me make something clear to Trump and his hatchet men," Biden said. "I'm not going anywhere."

That's what he says now. But look at the polls and then look at Biden's long slide from the front-runner position to a virtual tie with Warren. Biden has enormous hurdles ahead that have absolutely nothing to do with anything Trump says.