Mark Kelly, the astronaut-turned-Senate candidate, raised $4.2 million in the second quarter of 2019 for his bid to challenge Sen. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R-Ariz.).

That’s a staggering haul for a Senate candidate in an off-cycle year, surpassing the first quarter fundraising totals of even some presidential candidates.

Kelly’s second-quarter total came from nearly 100,000 contributions and 85,000 individual contributors, his campaign said Tuesday. Ninety percent of donations to the Arizona Democrat’s campaign were less than $100, and the average contribution was under $45.

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“This campaign started with a sonic boom just 140 days ago and it hasn’t slowed down,” Kelly campaign manager Jen Cox said. “We’re proving that when you elevate Arizonans’ voices over corporate PACs, people respond, they want to be part of this mission.”

Kelly is one of the highest-profile and most formidable Democrats challenging a Republican Senate incumbent in 2020. Since launching his campaign in February, he has raised roughly $8.3 million, his campaign said.

The Arizona Senate race is one of three Senate contests currently considered a toss-up by The Cook Political Report, along with races in Alabama and Colorado.

While Arizona has long been considered relatively friendly territory for Republicans, Democrats have become increasingly bullish on their chances in the state in recent years.

McSally, for instance, lost her initial Senate bid last year to Sen. Kyrsten Sinema (D-Ariz.) but was appointed by Arizona Gov. Doug Ducey (R) to fill the seat left vacant by the death of former Sen. John McCain John Sidney McCainAnalysis: Biden victory, Democratic sweep would bring biggest boost to economy The Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ariz.).