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With about two months left in the bruising 2016 presidential campaign, Donald J. Trump — the president-to-be who took on Gold Star parents and a federal judge, and seemed emboldened by the skirmishes — agreed to pause his campaign on the anniversary of the Sept. 11 attacks.

The unexpected show of decorum turned out to be a rare departure for President Trump, who has a history of using the Sept. 11 attacks to make political points, either by trying to burnish his own reputation or by damaging others’.

The most recent example came last week, when Mr. Trump circulated a video on Twitter to escalate his political attacks on Representative Ilhan Omar, the first-term Democrat of Minnesota who is also one of the first Muslim women to serve in Congress.

Using Sept. 11 to attack Representative Ilhan Omar

Mr. Trump posted a 43-second video that interspersed a snippet of speech from Representative Ilhan Omar alongside footage of the Sept. 11 attacks. His intent was to criticize what he apparently perceived as dismissive comments about the attack made by the congresswoman.