Polls have now closed in Maryland, where the high stakes of a Senate election have put intense scrutiny on the state’s primaries. Republicans have a rare opportunity to flip a Senate seat in Maryland in November, and the outcome of that race could determine control of the upper chamber.

Maryland voters cast ballots in the presidential race as well as congressional elections, and Joe Biden and Donald Trump easily won the state’s primaries after already securing enough delegates to capture their parties’ nominations.

Leaders of both parties were closely watching the results of the Senate contests, as the retirement of Senator Ben Cardin has created an opening for Republicans to potentially capture a seat in a reliably Democratic state, thanks to former governor Larry Hogan’s late entry into the race. A Hogan victory would mark the first time that a Republican has won a Maryland Senate election since 1980, and it could erase Democrats’ narrow majority in the chamber.

As expected, Hogan easily won the Republican primary, with the Associated Press calling the race less than an hour after polls closed. When the race was called, Hogan was capturing 68% of the Republican vote.

Ten Democrats competed for the party’s Senate nomination, but two candidates became the clear frontrunners: Congressman Dave Trone and the Prince George’s county executive Angela Alsobrooks. The race has historic implications, as Alsobrooks would become the first Black person elected to represent Maryland in the Senate and just the third Black woman to ever serve in the chamber.

Alsobrooks’s victory is far from guaranteed, as polls have shown her running neck and neck with Trone in the primary. Trone, the owner of the beverage chain Total Wine & More, used his personal fortune to boost his Senate campaign. According to documents filed with the Federal Election Commission, Trone loaned at least $61.8m to his campaign.

Trone pitched his ability to self-fund his campaign as a crucial asset for the general election, which has become unexpectedly competitive because of Hogan’s candidacy. When Hogan left office last year, a poll conducted for Gonzales Research & Media Services showed that 77% of Marylanders, including an astounding 81% of Democrats, approved of the governor’s job performance.

Hogan’s candidacy will force Democrats to allocate resources to a Senate race that they had previously assumed would be an easy win in the general election. In 2020, Biden beat Trump by 33 points in Maryland, but Hogan also won his 2018 re-election race by 12 points. Polls of potential general election match-ups have produced mixed results, but both parties will almost certainly have to spend heavily to compete in the state. The Cook Political Report currently rates the Maryland Senate race as “likely Democrat”.

After AP confirmed Hogan’s primary victory, Senate Democrats’ campaign arm quickly released a new digital ad highlighting the former governor’s self-description as a “lifelong Republican”.

“Hogan said it himself,” said Amanda Sherman Baity, spokesperson for the Democratic senatorial campaign committee. “A vote for Republican Larry Hogan is a vote to turn the Senate over to Republicans so they can pass a national abortion ban and push forward Republicans’ extreme policies. That’s a disqualifying agenda for Maryland voters.”

Elsewhere in the state, the Democratic primary in Maryland’s third congressional district turned increasingly contentious in recent weeks, after a Super Pac dropped millions of dollars into the race. Of the 22 Democratic contenders running to replace retiring congressman John Sarbanes, the former US Capitol police office Harry Dunn, who wrote a bestselling book about his experience protecting lawmakers during the January 6 insurrection, has the largest national profile. But polls showed a close race between him and state senator Sarah Elfreth, who won the backing of the pro-Israel Super Pac United Democracy Project.

Dunn, a first-time candidate, has proven himself to be a prodigious fundraiser, bringing in $4.6m across the election cycle. In comparison, Elfeth’s campaign raised just $1.5m, but she received outside help from UDP, which is affiliated with the American Israel Public Affairs Committee (Aipac). UDP spent at least $4.2m in support of Elfreth’s campaign, flooding the district with ads promoting her candidacy. Dunn turned UDP’s involvement in the race into a campaign issue, framing the “dark money spending” as corrosive to democratic principles.

The race to succeed Trone in representing Maryland’s sixth congressional district also attracted a crowded field of candidates. In the Democratic primary, the former Biden administration official April McClain Delaney and state delegate Joe Vogel have emerged as the frontrunners, while former state delegates Dan Cox and Neil Parrott were viewed as most likely to win the Republican nomination. Of Maryland’s eight congressional districts, the sixth is viewed as the most competitive for the general election, and Cook rates the seat as “likely Democrat”.

Although Biden and Trump have both already secured their parties’ nominations, Maryland’s presidential primaries could still offer clues about the general election. Biden’s name appeared on his party’s ballot alongside those of the Minnesota congressman Dean Phillips and self-help author Marianne Williamson, but Maryland Democrats also had the option to choose “uncommitted to any presidential candidate”.

Mirroring similar efforts in states like Michigan, pro-ceasefire advocates urged Maryland voters to cast ballots for uncommitted to protest against Biden’s handling of the war in Gaza. The Listen to Maryland campaign hopes that at least 15% of Democratic ballots were cast for uncommitted, and they reached out to hundreds of thousands of voters leading up to Tuesday.

In the Republican presidential primary, only the names of Trump and the former UN ambassador Nikki Haley appeared on the ballot. Although Haley dropped out of the race in March, she has continued to win votes in the weeks since, which has been viewed as a potential warning sign for Trump heading into the general election. In the Indiana primary held last week, Haley secured nearly 22% of the Republican vote, and leaders of both parties will be watching for a similar result in Maryland.