Former President Trump and meddling Democrats are both scrambling to get their preferred Republican candidate — businessman Bernie Moreno — over the finish line in Tuesday's Senate GOP primary in Ohio.

Why it matters: Democrats view Moreno as the weakest general election opponent for vulnerable Sen. Sherrod Brown (D-Ohio). Moreno is also the only Trump-backed Senate candidate at risk of losing in a GOP primary — a potentially embarrassing blow to the former president.

• Trump will rally with Moreno in a "surprise" visit near Dayton, Ohio, on Saturday, three days before the March 19 primary, according to a source familiar with the planning.
• Trump allies like Sen. J.D. Vance (R-Ohio), House Judiciary Chairman Jim Jordan (R-Ohio), South Dakota Gov. Kristi Noem and Arizona Republican Kari Lake will also head to Ohio this week.

Driving the news: Moreno is in a close contest with Ohio state Sen. Matt Dolan, who has the backing of establishment Republicans like Ohio Gov. Mike DeWine and former Sen. Rob Portman (R-Ohio).

• Moreno is currently a slight polling favorite in the race, according to FiveThirtyEight's average. But a poll from Emerson this week showed Dolan with a slight lead over Moreno.
• Ohio Secretary of State Frank LaRose is polling in a close third place.

The big picture: Dolan, whose father owns the Cleveland Guardians, has outspent Moreno. Despite endorsements from Trump and the conservative Club for Growth, Moreno has failed to solidify his spot as the front-runner.

Zoom in: Trump and his allies' visit to Ohio this week is an attempt to draw a clear distinction between the types of Republicans who are backing Moreno and Dolan.

• The juxtaposition of Moreno stumping with the likes of Trump and Vance is meant to serve as a "complete contrast" to Dolan's field of backers, a source familiar with the planning said.
• Vance, a potential VP pick, received a surge of support and ultimately won Ohio's competitive GOP primary in 2022 after he was endorsed by Trump.

The intrigue: A late splash of spending from outside groups shows how high the stakes are for Republicans — and for Democrats anxious to defend their slim Senate majority.

• Duty and Country PAC, a group tied to Senate Democrats, is spending $2.5 million on a TV ad highlighting Moreno's ties to Trump — seeking to boost him with the GOP's conservative base.
• A pro-Dolan super PAC placed a $1.9 million media buy on Monday opposing Moreno and LaRose, while the pro-Moreno Club for Growth spent over $830,000 on advertising on Tuesday.
• Dolan also personally gave his campaign another $1 million on Tuesday.

What they're saying: Sen. Gary Peters (D-Mich.), who runs the Senate Democrats' campaign arm, told Axios that the MAGA movement's support for Moreno shows he is a "weak candidate."

• "He's got out-of-staters coming in to campaign for him and Sherrod Brown always has people from Ohio campaigning for him," Peters said.