Since the start of the year, there have been $723 million worth of campaign ad buys for just three Senate races: in Ohio, Pennsylvania and Montana, according to AdImpact data.

• Why it matters: A fierce battle for control of the Senate is fueling the expected record-breaking ad spending this election cycle.

Zoom in: Democrats have long held a fundraising advantage over Republicans, which is helping them play defense in nine competitive Senate races.

• Ohio is the only Senate race in which Republicans have been spending more than Democrats on campaign ads and reservations, largely due to it having one of the only highly competitive Senate GOP primaries this year.
• Republican Bernie Moreno won the Ohio primary and will face Democratic incumbent Sen. Sherrod Brown in November.
• In Pennsylvania and Montana, the showdowns between Sen. Bob Casey (D) and Dave McCormick — and Sen. Jon Tester (D) and Tim Sheehy — come in second and third for ad spending and booking for both parties, so far.

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The senators vying to replace Sen. Mitch McConnell (R-Ky.) as GOP leader are packing their August recess with campaign travel and fundraisers as they jockey for votes from current and prospective colleagues.

Sen. John Thune (R-S.D.) flew to Wisconsin last week to fundraise with Eric Hovde, and then joined Dave McCormick's bus tour in Pennsylvania.

• He'll head to Utah, Nevada and Ohio in the coming weeks, according to a source familiar with his schedule.
• He has raised more than $19 million this cycle and will headline at least 170 events for candidates and the NRSC.

Sen. John Cornyn (R-Texas) has raised nearly $23 million this cycle through various apparatuses, according to a source familiar.

• Cornyn is also planning trips to battleground states, including Pennsylvania.
• "Sen. Cornyn is spending the summer doing what he's done for 15 years: crisscrossing Texas and the country to help his Republican colleagues and candidates, including President Trump," a Cornyn spokesperson told Axios.

Sen. Rick Scott (R-Fla.) will be spending most of his time in Florida, where he is up for re-election himself in a competitive state, a campaign spokesperson told Axios.

• Multiple Senate campaigns have neither heard from Scott nor received a check from him, sources familiar told Axios.
• His PAC has given tens of thousands of dollars this cycle to the NRSC and the campaigns of Moreno, Sam Brown in Nevada and Virginia's Hung Cao — as well as other less competitive Senate campaigns — according to a source familiar.

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A few Senate Democrats are rumored to be in the running for top posts under a potential Harris administration, according to conversations with a dozen senior Democratic sources and strategists.

Why it matters: Democrats don't expect many Cabinet holdovers from the Biden administration, and party strategists point to the Senate as an enticing pool of talent.

• Sens. Chris Coons (D-Del.) and Chris Murphy (D-Conn.) could be options for secretary of state, Democratic strategists tell Axios.
• Sen. Catherine Cortez Masto (D-Nev.) is a popular name floated for attorney general. She and Harris have a personal relationship dating back to their times as state attorneys general in neighboring states.
• Democrats also point to Senate Armed Services chair Jack Reed (D-R.I.) as a top candidate to lead the Defense Department.
• Sen. Martin Heinrich (D-N.M.) has also been floated for posts at the Departments of Education or Interior.

The bottom line: The outcome of Senate races in November will determine how willing Harris would be to tap senators for administration positions if she wins.

• For confirmation reasons, Harris could be expected to lean into senators and former senators if Republicans take the Senate.

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Above: Vice President Kamala Harris speaks at a campaign rally today in Eau Claire, Wisconsin. Her new running mate, Minnesota Gov. Tim Walz, also appeared at the event.

Below: Also in Eau Claire, GOP vice presidential candidate Sen. JD Vance speaks at NMC-Wollard Inc./Wollard International.