After spending most of the year disparaging each other from afar throughout the campaign for U.S. Senate in Arizona, Kari Lake, a Republican and close Trump ally, and Representative Ruben Gallego, a Democrat, wasted no time doing so again on their debate stage on Wednesday night.

Competing for the seat of Senator Kyrsten Sinema, who is retiring, Ms. Lake and Mr. Gallego focused on policy but also seized every opportunity to jab at each other by reminding viewers of past comments and positions.

Ms. Lake repeatedly accused Mr. Gallego of having undergone “an extreme makeover,” shifting from a progressive member of the House to a more moderate lawmaker whose views are more palatable to the majority of Arizonans, including the Republican voters Mr. Gallego is actively wooing. And she sought to skewer him on immigration, accusing him of being soft on the border.

“Ruben Gallego has supported — every step of the way — Kamala Harris, the border czar, and Joe Biden’s open border,” Ms. Lake said.

Mr. Gallego, who has worked to tack more toward the middle in the past year, especially on immigration, also talked tough, saying he was proud of votes during his time in Congress to bring more border agents to Arizona. He also hit back, accusing Ms. Lake of opposing a bipartisan border security bill for political expediency.

“You’ve been to Mar-a-Lago more than you have been to the border,” Mr. Gallego said at one point, referring to former President Donald J. Trump’s Florida resort.

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