LIVE UPDATES: Follow the results of Oklahoma's June 30 primary elections

• Oklahoma is holding primaries for US Senate and all its US House of Representatives districts on June 30.
• The most notable race to watch will be the crowded Republican primary in Oklahoma's fifth congressional district to challenge vulnerable Democratic Rep. Kendra Horn.
• Due to the high volume of voters casting ballots by mail this election, the race may not be called until after election day.

The stakes:

The most notable Oklahoma primary this week will be the Republican primary for Oklahoma's fifth congressional district, a highly competitive swing district currently held by Rep. Kendra Horn, the sole Democrat in Oklahoma's congressional delegation.

Horn was elected in the 2018 midterms to the district, which includes parts of Oklahoma City and the surrounding suburbs, by a margin of 1.4 percentage points in an upset win over GOP Rep. Steve Russell. President Donald Trump carried the district by 13.4 percentage points in the 2016 election.

—Drew Savicki (@SenhorRaposa) April 18, 2019

The crowded primary field to challenge her this November includes State Senator Stephanie Bice, former Superintendent of Public Instruction Janet Barresi, businesswoman Terry Neese, and auto parts manufacturing executive David Hill.

Currently, Bice leads the primary field in fundraising with over $1 million raised and over $228,000 in cash-on-hand. She's followed by Neese, who has raised over $981,000, including $450,000 she lent to her own campaign, the Center for Responsive Politics reported.

While Horn may be one of the most vulnerable House Democrats, she's built up a formidable war chest of campaign funds with $3.2 million raised so far this cycle and $2.4 million in cash-on-hand.

Oklahoma is a runoff state, meaning if that no one candidate receives over 50% of the vote in Tuesday's primary, the race will go to a runoff between the top two vote-getters on August 25.