Donald Trump Jr. plans to travel to Georgia by the end of the month to urge Republicans to turn out for twin Jan. 5 runoffs that'll determine control of the U.S. Senate, and will argue that the outcome is crucial to cementing his father's legacy.

Why it matters: Republicans worry that President Trump's grievances about the last election could keep his voters home for the next one. Don Jr., who did 100 campaign events between Sept. 1. and Election Day, has huge credibility with the base.

Save the U.S. Senate PAC is spending $500,000 on its debut TV ad, with Don Jr. saying: "My father's accomplishments are on your ballot."

• The ad will run statewide digital and Fox News in Georgia, and nationally on Newsmax.

The super PAC, which launched last week with a six-figure radio buy, was started by two close Don Jr. advisers, Andy Surabian and Taylor Budowich,

• Save the Senate has filmed a second Don Jr. ad with a Second Amendment focus. That ad will debut later this month.

Don Jr. told Fox News' Tucker Carlson on Tuesday night that Democrats would love for Republicans to be demoralized: "If you sit back and allow apathy to take over, ... you are literally giving the Democrats everything that they have hoped for."

• "My father's legacy ... everything that he's accomplished is on the table, as far as I'm concerned, in this election," Don Jr. continued.
• "So if you're a Trump guy, you'd be foolish to listen to a few individuals who say: 'Ah, sit at home.' It's as though they're working for the Democrats."

Go deeper: Watch the ad