DES MOINES — Former President Trump — who for months has appeared to be coasting to a big win in Iowa's caucuses — is showing signs of worry ahead of Monday night's voting.

Driving the news: Trump is escalating his attacks on Nikki Haley and imploring his supporters to brave Monday's wickedly cold weather to vote as if he's trailing in the polls.

• It's the latest indication of urgency from the former president, who now sees his former UN ambassador as his chief threat in the Hawkeye State and beyond.

Zoom in: Trump's team also is lowering the bar for what it would consider a success in 2024's first presidential contest.

• Since the fall, Trump has had polling leads in Iowa of more than 30 points over Haley, Florida Gov. Ron DeSantis and Vivek Ramaswamy.
• But Friday, Trump senior adviser Chris LaCivita reminded reporters at a Bloomberg roundtable that no one's ever won the Iowa caucuses by "more than 12.8%" — and that he'd count a Trump win by more than that as a success.

Trump's team — like other campaigns — has shown some anxiety over how Iowa's brutally cold weather might affect voter turnout on Monday, when temperatures are predicted to be as low as -13°F.

• In recent days Trump and his son Don Jr. have urged Iowa crowds to pretend the former president is behind in Iowa, and to do everything they can to make sure they vote.

Between the lines: If Haley finishes a reasonably strong second to Trump in conservative Iowa, she'd be set up for success in the Jan. 23 primary in more moderate New Hampshire, where polls indicate she trails Trump only by single digits.

• The possibility of Haley gaining more momentum has made her the top target of the Trump and DeSantis campaigns in the closing days of the Iowa race.

State of play: Trump's team is stepping up its criticism of Haley this week, claiming she's weak on border security, would seek higher taxes and is propped up by donations from Democrats.

• Trump aides are pushing the notion that "life could be much difficult and much more expensive" under Haley.
• Another sign Trump sees Haley as a threat: He's trying to insult her with a nickname, just as he's done with several other political opponents.
• This week, Trump's been calling Haley "Nikki New Tax."
• Trump also has turned to some of the race-baiting tactics he's used in criticizing former President Obama — falsely suggesting that Haley shouldn't be eligible to be president because of her parents' heritage as Indian immigrants.

Trump's campaign is taking aim at Haley's calls to change Social Security — such as by raising the retirement age for workers who are now young — to ensure the program's long-term survival.

• Trump's team released an ad that begins: "Americans were promised a secure retirement. Nikki Haley's plan ends that."
• The main pro-Trump super PAC ran millions of dollars in ads on the issue last spring that were widely seen as hurting DeSantis' poll numbers.

What they're saying: Trump "has always said he's going to train the sights on second place, and just as (DeSantis) implodes as a candidate, we're going to start calling out (Haley's) record," Trump senior adviser Jason Miller said.

The other side: "All of Donald Trump's attack ads prove that he is terrified of Nikki Haley's rise," Haley communications director Nachama Soloveichik said.

• "This is a two-person race between Nikki's conservative vision for a strong and proud America, and Trump's continued obsession with the chaos and drama of the past."

Alex Thompson reported from Washington.