(YAHOO) — Donald Trump tweeted on Tuesday that “the shackles have been taken off” his campaign — a thinly veiled threat suggesting that the final 28 days of the presidential race will be filled with personal attacks. That scorched-earth strategy is on full display in the Trump campaign’s latest ad, which targets Hillary Clinton’s health.

“Our next president faces daunting challenges in a dangerous world,” a voice-over says at the beginning of the 30-second spot. “Iran promoting terrorism; North Korea threatening; ISIS on the rise; Libya and North Africa in chaos. Hillary Clinton failed every single time as secretary of state. Now she wants to be president.”

The ad then cuts to clips of Clinton earlier in the campaign, coughing on the stump and being helped onto her plane and into her van.

“Hillary Clinton doesn’t have the strength, stamina or fortitude to lead in our world,” the narrator continues over an image of her checking email on her BlackBerry. “She failed us as secretary of state. Don’t let her fail us again.”

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