Philadelphia, Pennsylvania - Donald Trump on Saturday said that he has decided on a running mate for the US presidential election in November, but has not yet told anyone about it.

Trump travelled to Philadelphia for a campaign rally and beforehand stopped off at a steak restaurant, where he was cheered by supporters and also answered a few questions from reporters.

When asked by whether he had made his pick for vice president, Trump replied: "In my mind, yeah," before adding that "nobody knows" yet what his decision is.

Among the many names touted as Trump's possible running mate are Senators JD Vance, Tom Cotton, Marco Rubio, and Tim Scott, as well as Florida Representative Byron Donalds and South Dakota Governor Kristi Noem.

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The Republican's campaign has been reportedly vetting candidates over the past weeks.

Before his trip to Philadelphia, Trump courted the evangelical Christian vote with an appearance at an event organized by the Faith and Freedom Coalition in Washington DC.

President Joe Biden, meanwhile, was spending the weekend at Camp David near Washington to prepare for the televised debate with Trump set for Thursday.

Trump's nomination won't be official until the Republican Party Convention in Milwaukee, Wisconsin, in July. The Democrats will officially select their candidate in Chicago in August.