A group of super PACs supporting Republican presidential candidate Ted Cruz released an ad attacking rival Marco Rubio. (Keep the Promise)

The well-financed super PACs supporting Ted Cruz are launching a $1 million advertising blitz this week to boost the Texas senator — and cast his rival, Marco Rubio, as unserious and unready.

This latest salvo by affiliates of Keep the Promise, the umbrella moniker of several Cruz-allied groups, aims to chip away at Rubio’s support among conservatives in early-voting states, in particular by sullying the Florida senator’s profile as a hawkish and mature voice on foreign affairs.

The super PACs’ first television ad – which is titled “Leadership” and was shared Monday with The Washington Post – unsubtly portrays Rubio as a distracted, fantasy-football devotee who checks scores as tumult and terror erupt across the globe.

Keep the Promise I, one of the Cruz super PACs, is paying for the bulk of the $750,000 television campaign that will air for two weeks in Iowa starting Jan. 5, according to its representative. Other Keep the Promise groups will spend about $250,000 in the coming weeks on radio and digital buys to promote the 30-second ad.

While television viewers in Iowa, where Cruz is campaigning this week, are the initial target audience, digital and radio buys have been made there and in New Hampshire, South Carolina and Nevada. That element of the groups’ anti-Rubio campaign will include a radio ad that touts Rush Limbaugh’s praise of Cruz and notes his opposition to the immigration legislation that Rubio once backed.

Cruz is never seen or cited in the “Leadership” spot. Instead, it begins with a fast-cut montage: Islamic State militants, a refugee crisis in Syria, a growing relationship between Russia and Iran. Then there is a question: “What would Marco Rubio’s leadership look like?”

Rubio appears, jacket off and hunched over his laptop. He’s on the phone and smiling. “Yeah, I know I have a debate,” he tells a caller. “But I’ve got to get this fantasy football thing right. Okay?”

Suddenly, as pulsing beats are heard, the following message is splayed across the screen in staccato, chunky-lettered bursts: “Tell Marco Rubio: America can’t afford to gamble with its safety.”

What’s unmentioned is that the Rubio clip comes from a humorous video the Rubio campaign published last October ahead of CNBC’s Republican presidential debate.

Matthew Taylor, a filmmaker who worked on ads for Mitt Romney’s 2012 campaign, produced the ad for the Cruz super PAC.

The battle between Rubio and Cruz for conservative hearts has only intensified in recent days as both have largely avoided clashes with the GOP front-runner, Donald Trump, and focused their attacks on each other, especially over matters of national security and immigration.

In a speech Monday in Hooksett, N.H., Rubio did not name Cruz but attacked “isolationist candidates who are apparently more passionate about weakening our military and intelligence capabilities than about destroying our enemies.”