(CNN) All three Republican primary challengers lambasted state GOP leaders -- and President Donald Trump -- for opting to cancel their 2020 presidential primary elections in a show of support for the President.

"In the United States, citizens choose their leaders," former Rep. Mark Sanford of South Carolina, former Rep. Joe Walsh of Illinois and former Massachusetts Gov. Bill Weld said in a Washington Post op-ed on Friday.

"The primary nomination process is the only opportunity for Republicans to have a voice in deciding who will represent our party," they added. "Let those voices be heard."

Their pushback comes after party leaders in Kansas South Carolina and Nevada canceled their Republican primaries, with Arizona expected to make it official over the weekend. The scrapped primaries pose a further obstacle for the long-shot challengers, already fighting the incumbent President, who, according to a CNN/SSRS Poll, has an 88% approval rating among Republicans.

It is not unprecedented for state Republicans or Democrats to decide not to hold a presidential primary when an incumbent is running essentially uncontested. In South Carolina, a key early primary state, Republicans decided to nix their presidential primaries in 1984 and 2004, when Ronald Reagan and George W. Bush were up for their second terms, while state Democrats skipped their contests in 1996 and 2012, with Bill Clinton and Barack Obama running for reelection.

Read More