Democratic presidential candidate Julián Castro rolled out a five-figure ad buy in Iowa on Tuesday as he seeks to sharpen his case that he is the right candidate to take on President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE in 2020.

The ad comes as the former Housing and Urban Development secretary prepares to lay off campaign staff in New Hampshire and South Carolina, while doubling down on his efforts in Iowa and Nevada in a last-ditch bid to gain momentum ahead of the first-in-the-nation caucuses.

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“I’m asked often: ‘How can we beat Donald Trump?’ ” Castro says in the ad, which is set to be released on social media on Tuesday. “It’s a challenge I don’t take lightly. In the face of his cruelty, I’ve sought justice. To answer his failings, I’ve been bold. To address his corruption, I’ve been clear. To counter his lies, I’ve sought hope.

“He’ll never understand what makes this country great — what makes a story like yours and mine possible. This country belongs to all of us.”

The $50,000 ad buy reflects Castro’s efforts to remain in the race for the Democratic presidential nomination at a time when his campaign is struggling. The decision to fire staff in New Hampshire and South Carolina, two critical early primary states, was first reported on Tuesday by Politico.

National and early-state polls have shown Castro for months lingering in the low single digits, and he has failed to raise the kind of money that his top-tier rivals have. In the third quarter of the year, he raked in just under $3.5 million but spent nearly $4 million, meaning he is burning through money at a faster rate than he is raising it.

In laying off his staff in New Hampshire and South Carolina, Castro is hoping to bolster his operations in Iowa, Nevada and his home state of Texas, which holds its primary on Super Tuesday.

He’s not the first candidate to begin laying off staff and shifting resources to Iowa. Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE’s (D-Calif.) campaign said last week that it would cut staff in its Baltimore headquarters and redeploy aides in New Hampshire and California to Iowa in hopes of bolstering its operation there.