Martha MacCallum will interview Department of Homeland Security Secretary Kirstjen Nielsen Thursday on The Story, as the massive migrant caravan moves closer to America's southern border.

The caravan has become a major talking point for Republicans with midterm elections less than two weeks away.

It has reportedly grown to about 7,000 people as of Monday, and most of the migrants within it have come from Honduras, according to reports.

Nielsen said in a statement last weekend that the DHS will work with its regional partners to monitor the caravan for potential criminals.

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President Trump on Monday doubled down on his contention that terrorists could have infiltrated the caravan, calling it "a horrible thing."

He told a reporter to "go into the middle of the caravan and take your camera and search" for the suspected terrorists, after the reporter challenged the president on the notion.

Later in the day at a rally in Texas, Trump pointed to the caravan as one of the country's major concerns ahead of the midterms.

"This will be the election of the caravan, [Supreme Court Justice Brett] Kavanaugh, law and order, tax cuts and common sense," he told the crowd in Houston.

Nielsen had also tweeted last week that "every available measure" will be used to prevent any type of illegal entry into the United States.

Don't miss the conversation on The Story with Martha MacCallum, tomorrow night at 7 p.m. on Fox News Channel.

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