'Start Here': Rick Gates, primaries and Indra Nooyi. What you need to know to start your day

It's Tuesday, Aug. 7, 2018. Here are some of the stories we're talking about on ABC News' new daily podcast, "Start Here."

1. Mueller's star witness takes the stand

Rick Gates was Paul Manafort's right-hand man when he was lobbying on behalf of foreign governments and running the Trump campaign, but yesterday Gates took on a new role as special counsel Robert Mueller's star witness.

Gates testified against his former business partner in federal court, admitting he engaged in criminal activity with Manafort in the years he spent by his side. While Gates has pleaded guilty to federal charges, Manafort has maintained his innocence, and ABC News' Trish Turner -- who has been watching the trial in Alexandria, Virginia -- tells us it's all part of Gates' plea deal with Mueller.

"He has to tell the truth here or every bit of the charges that were against him that have been forgiven will all snap back. It's pretty key."

"Start Here" is a daily ABC News podcast hosted by Brad Mielke featuring original reporting on stories that are driving the national conversation. Listen for FREE on the ABC News app, Apple Podcasts, TuneIn, Spotify, Stitcher, Google Play Music, iHeartRadio -- or ask Alexa: "Play 'Start Here.'"

Follow @StartHereABC on social for exclusive content, show updates and more: Twitter, Facebook, Instagram.

2. 2018 midterms: Four primaries and a special election

Kansas, Michigan, Missouri and Washington will hold primary elections today while voters in Ohio's 12th Congressional District will cast their ballots in the last special election before Republicans and Democrats face off in November.

President Donald Trump won OH-12 by 11 percentage points in 2016, so why is the GOP so concerned about the race? ABC News' Adam Kelsey tells us from New Albany, Ohio, "There are a lot of Republicans out here that aren't big fans of President Trump."

ABC News Political Director Rick Klein and ABC News Deputy Political Director MaryAlice Parks also join us in-studio to review what else they're tracking tonight.

3. US reimposes sanctions on Iran

During the Obama administration, an agreement was reached with Iran to lift sanctions if the country rolled back its nuclear program. Trump was never a fan of the Iran nuclear deal and in May he decided to back out of it.

The decision finally took effect at midnight on Tuesday and ABC News' Conor Finnegan, who covers the U.S. State Department, tells us what happens next.

4. PepsiCo's first female CEO, Indra Nooyi, steps down

Indra Nooyi will step down as the CEO of PepsiCo after 12 years, leaving behind a legacy for women entrepreneurs and a company that nearly doubled its revenue and share price under her leadership.

But during a time when there are fewer female executives than there were last year, her male replacement, Pepsi President Ramon Laguarta, has raised eyebrows.

"There is a path to CEO and not enough women are on it," ABC News Chief Business and Economics Correspondent Rebecca Jarvis says.

5. 911 call centers need more workers

Several 911 call centers across the country are having trouble finding people to work the phones, which means fewer emergencies are being connected to police, firefighters and ambulances.

Deanna Wells runs a 911 center in Cowlitz County, Washington, and she thinks one of the reasons why there are less applicants is because of the low unemployment rate: "There are fewer [applicants] and they have better options."