Arizona Republicans told state election officials Monday they're scrapping their 2020 primary, joining GOP leaders in three other states that are forgoing a presidential nominating contest as President Trump seeks re-election.

Longshot candidates challenging Mr. Trump for the Republican nomination have objected to the moves in Nevada, South Carolina and Kansas to skip GOP primaries or caucuses next year.

"Arizona Republicans are fired up to re-elect President Trump to a second term and will continue to work together to keep America_and Arizona_great," State GOP Chairman Kelli Ward said in a statement last week.

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Challengers to Mr. Trump have emerged, including former South Carolina Governor and Representative Mark Sanford, former Massachusetts Governor Bill Weld and Joe Walsh, a former Illinois congressman.

Primary challenges to incumbents are rarely successful, and Trump's poll numbers among Republican voters have proved resilient.

Nonetheless, Trump aides are looking to prevent a repeat of the convention discord that highlighted the electoral weaknesses of Presidents George H.W. Bush and Jimmy Carter in their failed reelection campaigns.

States have until October to submit their delegate selection rules to the Republican National Committee, and several more state Republican parties could vote to cancel their nominating contests before the deadline.

Chairwoman Ronna McDaniel told CBS News last week that the Republican National Committee does not dictate whether the state parties should hold nominating contests. That decision is left to the states. However, Mr. Trump's re-election campaign has dispatched its delegate staff to many of the GOP state conventions where they have observed chair elections and advised on delegate selection rules.

Eleanor Watson contributed to this report.