• Republicans revisiting party rules for filling vacancies after Trump's erratic week
• Plan would only work if Trump were to remove himself from the ballot
• Officials fuming over candidate's refusal to endorse Speaker Paul Ryan, who has a primary challenge and his spat with the family of fallen hero Humayun Khan
• Trump said Tuesday he wasn't 'there yet' on Ryan, mimicking language Ryan used when holding off on Trump endorsement
• He's also refusing to back Arizona senator John McCain
• If Trump were to quit, 168-member RNC would meet to pick successor
• Trump said election might be 'rigged,' tangled with gold star parents, gleefully accepted a Purple Heart and joked about how easy it was to get, and urged a mom to take her crying baby out of his rally – all in one day!
• Trump accepted the GOP nomination in Cleveland last month

Slack-jawed senior Republican officials are so incensed at Donald Trump's recent performance that they are actively exploring how to replace him on the ballot were the real estate mogul to drop out of the race.

'Senior party officials' are so upset with his behavior that they are exploring how to replace him on the ballot, ABC News reported.

CNN reported that Priebus was 'extremely upset' with Trump's refusal to endorse House Speaker Paul Ryan and his handling of a dispute with the Khan family – an issue where Ryan distanced himself from Trump.

NBC reported that Priebus was 'apoplectic,' while ABC called him 'furious.'

Priebus called Trump Tuesday to express his frustration with how his spat with the family of slain Army Captain Humayun Khan has distracted the campaign since the end of the Democratic convention, where Khan's father spoke, according to ABC.

An official told CNN he was examining what the rules were in the event of a vacancy.

There have been no indications from Trump that he plans to get out of the race.

Priebus is also a Wisconsin native close to Paul Ryan, who is facing a primary challenge on Tuesday.

No matter the fury some Republicans might be feeling toward Trump – whose election is closely linked to their own ability to keep majorities in the House and Senate – the methods for replacing him are complicated.

To do so, he would have to drop out, and for mechanical reasons this might have to happen by September, as ABC described the scenario.

Republican National Committee rules state that the committee 'is hereby authorized and empowered to fill any and all vacancies which may occur by reason of death, declination, or otherwise of the Republican candidate for President of the United States or the Republican candidate for Vice President of the United States.'

In such an instance, the 168-member RNC would reconvene the party's national convention to fill the vacancy.

The replacement would be chosen by the panel, which consists of state chairs and party leaders.

The members members representing a state 'shall be entitled to cast the same number of votes as said state was entitled to cast at the national convention.'

A candidate would only win after getting a majority of the votes entitled to be cast.

John Harwood of the New York Times tweeted Tuesday night that Trump campaign chairman Paul Manafort was 'mailing it in' and not challenging Trump anymore, and that staff were 'suicidal.'

Trump tweeted Wednesday: 'There is great unity in my campaign, perhaps greater than ever before. I want to thank everyone for your tremendous support. Beat Crooked H!'

Trump told the Washington Post he wasn't ready to back Ryan, the party's 2012 vice presidential nominee and a popular figure within the party. 'I'm just not quite there yet. I'm just not ready to do that at this point,' he said.