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.

A disappointing finish in the state, where there are four candidates bunched in the top tier in polls, could dampen his fund-raising at a crucial juncture. Candidates need resources to build up their operations in delegate-rich Super Tuesday states like California, where campaigning and ad rates can be prohibitively expensive and early voting begins next week.

DES MOINES, Iowa (AP) — Bernie Sanders was endorsed Thursday by the 200,000-member American Postal Workers Union, an influential group that also backed the Vermont senator’s presidential bid against Hillary Clinton during the 2016 Democratic presidential primary.

The union’s support is key because it promises organizing muscle across the country. Sanders says that if turnout is high during Monday’s lead-off Iowa caucus, he will win — and a win there will key victories in the next two states that vote, New Hampshire and Nevada.

“As with 2016, once again the Sanders campaign is boldly uplifting the goals and aspirations of workers,” union president Mark Dimondstein said in a statement. “Simply put, we believe it is in the best interests of all postal workers, our job security and our union to support and elect Bernie Sanders for president.”

Polls in Iowa and other states show Sanders bunched near the top of the polls with former Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren and Pete Buttigieg, the former mayor of South Bend, Indiana.

Sen. Bernie Sanders (I-Vt.) is considering dozens of executive orders he could unilaterally enact on a wide range of domestic policy issues if elected president, including immigration, the environment and prescription drugs, according to two people familiar with the campaign’s planning and an internal document reviewed by The Washington Post.

Sanders has risen in national and early-state polling in the final days before Monday’s Iowa caucuses, the first contest in the Democratic presidential primary, which has fueled concerns among some party insiders that he could win the nomination.