Michael Alfonso, 26, son-in-law of President Donald Trump's transportation secretary, Sean Duffy, has won the GOP nomination for Wisconsin's 7th Congressional District. 

Duffy previously represented the seat in northern Wisconsin from 2011 to 2019.

Alfonso is married to Evita Duffy-Alfonso, also 26, who is the eldest daughter of the transportation secretary and his wife, Fox News host Rachel Campos-Duffy.

Alfonso beat out Jessi Ebben, Kevin Hermening, Niina Threlfall-Baum and Cheryl Ann Runkel, who were running on the GOP ballot. 

Trump backed Alfonso in a Truth Social post, calling it a 'great honor' to endorse the 26-year-old, whom he called a MAGA warrior and a young 'STAR.'

The president touted his support for energy dominance, the Second Amendment, and border and election security as reasons Republicans should support him.  

During the bitter primary battle, Alfonso was criticized for his young age and the significant impact his in-laws were making in the race.

Meg Ellefson, a podcaster and prominent former drive-time radio show host in Wisconsin, hit Duffy for 'exploiting his Cabinet position and fame to influence an election and hand one of the nation's offices to his unqualified, 26-year-old son-in-law.' 

Ellefson added that she was 'utterly disgusted by this blatant manipulation of voters' and is backing one of Alfonso's primary rivals.

Critics have pointed to campaign contributions Alfonso has received from transportation interests, suggesting those donations were made to lobby Duffy.

Transportation spokesperson Nathaniel Sizemore told the Daily Mail back in June that Duffy follows the rules before attending any campaign or fundraising events on behalf of his son-in-law, and that his campaign work has been in his personal capacity.

'Before attending any event, career ethics officials at USDOT screen these events, review the hosts, advise on attendees, and provide recommendations that Secretary Duffy follows,' Sizemore told the Daily Mail. 'These processes and rules have existed for decades.'

'Whether it's installing a brand-new air traffic control system, transforming Penn Station, kicking dangerous truck drivers off the roads, or making cars more affordable again, Secretary Duffy uses the power of DOT to execute on the President's ambitious transportation agenda. That's it,' Sizemore added.

The vacancy for the seat was created after GOP Congressman Tom Tiffany chose to run for governor in a primary contest, which he also won on Tuesday.

Wisconsin's 7th congressional district is considered to be a GOP stronghold, and it has been represented by Republicans for the last 15 years.