Arizona Democratic candidate and former astronaut Mark Kelly raised $12.8 million in the second quarter, campaign officials said Tuesday. Kelly, the husband of former U.S. congresswoman Gabby Giffords, is bidding to unseat incumbent Sen. Martha McSally, R-Ariz., in one of the most hotly contested races in the country.

Of the nearly $13 million raised by Kelly’s campaign, 89% of the contributions came from donations smaller than $100, with the average donation coming in at $44.

“We continue to be humbled by the hundreds of thousands of people chipping in whatever they can, because they want to see Mark Kelly’s experience and independent approach representing Arizonans – defending health care protections for those with pre-existing conditions and fighting for our state in the U.S. Senate,” Kelly’s campaign manager Jen Cox said about the fundraising.

Kelly’s campaign has $24 million in cash reserves. McSally’s campaign has not yet published its fundraising totals for the second quarter of the year.

Kelly, 59, previously worked for NASA as an astronaut and began his career as a naval aviator. He has never served as an elected official. Giffords, who served in the House from January 2007 to January 2012, was shot in an assassination attempt in 2011. Giffords survived the shooting, with the couple now pushing for stronger gun safety measures.

McSally, a 54-year-old former Air Force pilot, has served in the Senate since January 2019, and was appointed to her seat after Sen. Jon Kyl resigned by Arizona Gov. Doug Ducey, a Republican.

In 2018, McSally had run for the other Senate seat in Arizona, which had been occupied by Sen. John McCain, but lost to Democratic candidate Kyrsten Sinema. This year’s Senate race will determine whether McSally will be able to complete the last two years of her term.

The latest poll from OH Predictive Insights shows Kelly with 52% of the vote, to McSally’s 43%. A CBS News/YouGov poll shows Kelly at 46% and McSally at 42%.

Arizona is a valuable state for the Democrats in their quest to obtain a Senate majority. Democrats will need to pick up three to four seats this election to take the Senate, depending on which party seizes the White House.