DES MOINES — Joseph R. Biden Jr.’s campaign has quietly rolled back hundreds of thousands of dollars of television ad reservations in New Hampshire and South Carolina in recent weeks and redirected the funds to buy more ads in Iowa instead.

Mr. Biden’s campaign and a super PAC supporting him are on pace to churn through nearly $9 million on television ads in Iowa ahead of the caucuses on Monday, while spending virtually nothing so far in the other three states that vote in February. Mr. Biden has also planted himself in the state this week, seizing on the Senate impeachment trial and President Trump’s rally in Des Moines on Thursday night to try to convince voters that Republicans are scared to run against him.

The movement of money and energy into Iowa is a sign of not only the opportunity that Mr. Biden’s campaign now sees here — he sits in second or first place in most polls — but also the acute risk for him, according to interviews with Democratic strategists, Biden fund-raisers and allies.

In Iowa, Mr. Biden is not just chasing votes and delegates. He’s chasing cash.

It took years before I became perceptive enough to see something more important, something I hope others watch Monday night.

They’ll see a tradition that others mock. New Hampshirites say, “Iowa picks corn. We pick presidents,” pointing out that finishing first in Iowa doesn’t mean a clear road to the White House. It doesn’t; in the past six elections, Iowa Democrats have picked presidents just 50 percent of the time.

But Iowans caucus to pick nominees. In those six elections, Iowa Democrats picked their party’s nominee each time. A win Monday night is a big deal. Even fourth place keeps a Democratic candidate alive.

Critics are right about other problems. They argue that the caucuses are not “inclusive,” ignore independents, sacrifice substance for organizing, and turn out far too few voters.

All true. But except for turnout, an Iowa primary would be flawed in the same way. Primaries turn out more people — 29 percent of eligible voters nationally to Iowa’s 16 percent in 2016. But turnout, pathetically low for both caucuses and primaries, reflect the abysmal way the United States conducts elections more than flaws in the caucus system. There are many ways to fix that — and other countries have. Still, in one OECD 35-country study of turnout, the U.S finished 31st. Our system cries out for reform.

Even if reform comes, though, Iowa should keep the caucus — especially in this era when so many Republicans and Democrats hate each other.

Mike Bloomberg's presidential campaign is predicated on Joe Biden's collapse.

But Biden has steadied his wobbly bid heading into the Iowa caucuses, sending the two moderates toward a likely Super Tuesday collision.

The emerging battle has those in both camps looking over their shoulders — with Biden seeking to claim the center mantle by gaining unstoppable momentum from the early states and Bloomberg's sprawling operation prepared to pick up the pieces should he falter or seem too weak to win.

Bloomberg’s aides continue to express concerns that Biden and the rest of the Democrats competing in the early states would lose to Trump. They view it as increasingly likely that there will be muddle coming out of South Carolina. And they see Bloomberg’s behemoth organization, growing stable of Super Tuesday endorsements and ability to stretch the map with limitless cash as giving him the edge.

DES MOINES—It was late summer, and Elizabeth Warren was sitting pretty. The closely watched Iowa Poll, conducted by Ann Selzer for the Des Moines Register, showed Warren at the top of the Democratic presidential field. She was flush with cash. The organizational juggernaut her campaign had built was widely lauded. Insiders here were calling her the prohibitive frontrunner. And she had yet to air one TV ad in Iowa.

This wasn’t an oversight. It was a strategy. From mid-August until late October, when her rivals were flooding the airwaves, Warren would remain dark on TV for 12 weeks. Her first ad on broadcast TV ran on Oct. 26, long after she had risen to the top of the field.

Beginning in mid-August, Pete Buttigieg pretty much took the opposite approach. The mayor of South Bend, Indiana, spent $2 million on TV and radio ads during the same 12-week period. He had run five different spots by the time Warren appeared on television for the first time. When November’s Iowa Poll was released, at the end of that 12-week run, the small-town mayor with the funny name was in first place—and the Des Moines Register heralded him as “a clear frontrunner.”

Since that moment, the race’s dynamics have shifted again and again, and heading into the last weekend before the Iowa caucuses, most observers consider it a four- or even five-way race that’s too close to call. Once Iowa Democrats make their choice on Monday night, pundits are sure to use the results to try to settle any number of intra-campaign disputes, including whether Amy Klobuchar’s Iowa-focused strategy paid off, and whether Joe Biden and Bernie Sanders lived up to their sky-high name recognition during what must be each man’s final shot at the presidency. But among campaign staffers and media strategists, the caucuses will also serve as a referendum for a crucial question in the dark arts of campaign messaging: What’s the most effective way to reach voters in 2020? Should campaigns go heavy on digital spending, or do it the old-fashioned way, on TV?