US presidential candidates Donald Trump and Kamala Harris are at odds over their first head-to-head debate, with each in favour of a different broadcaster and date.The Harris campaign is pushing for a debate to take place on ABC News on 10 September, in a slot previously scheduled for a debate between President Joe Biden and Mr Trump.But Mr Trump says the ABC debate has been “terminated” by Mr Biden leaving the race – and has instead pushed for himself and Ms Harris to debate on Fox News on 4 September.The pair will face off for the presidency when the US goes to the polls on 5 November.The disagreement began after President Biden dropped out of the race on 21 July, with Ms Harris immediately becoming favourite to secure the Democratic nomination.Since then, Mr Trump has been non-committal about whether he will still take part in the previously scheduled ABC News debate.US TV networks have been negotiating with both campaigns to arrange new dates.On Friday night, Mr Trump wrote on his social network Truth Social that he had accepted Fox News’ proposal for a debate on 4 September, which is pencilled to take place in Pennsylvania – a key battleground state.He wrote that the moderators would be Fox News’ Bret Baier and Martha MacCallum – and that the rules would be similar to his debate with Mr Biden.”If for any reason Kamala is unwilling or unable to debate on that date, I have agreed with Fox to do a major Town Hall on the same September 4th evening,” he wrote.The Harris campaign hit back, saying: “Donald Trump is running scared and trying to back out of the debate he already agreed to and running straight to Fox News to bail him out.”“He needs to stop playing games and show up to the debate he already committed to on Sept 10,” Michael Tyler, Harris Campaign communications director said. Ms Harris secured enough pledges to become the Democratic nominee on Friday.During a campaign rally in Atlanta on Wednesday, Ms Harris challenged Mr Trump to debate her, saying “if you got something to say, say it to my face”.The debate news comes just hours after a report by the Homeland Security Department revealed that the US Secret Service made mistakes in their response to the 6 January attack on the US Capitol.Ms Harris, who was then vice-president-elect, came within 20ft (6m) of a “viable” pipe bomb planted outside the Democratic National Committee’s headquarters in Washington.That bomb – and a similar one found at the Republican National Committee headquarters – were placed near the buildings the night before Trump supporters stormed the US Capitol. It remains unclear who planted both pipe bombs.