Washington DC - Donald Trump's online store is selling clothing emblazoned with "Trump 2028," the year of the next presidential election, in which the Republican is constitutionally banned from running.

The 78-year-old, who has seen his approval rating sink in recent opinion polls, has not ruled out serving a third term – though most spectators consider that highly unlikely.

A social media account linked to Trump shared a photo Thursday of his son Eric sporting one of the new red caps, which is priced at $50.

"Make a statement with this Made in America Trump 2028 hat," a product description on the Trump Store website says.

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The shop is also selling t-shirts in navy and red, priced at $36, which read "Trump 2028 (Rewrite the Rules)."

It comes as Trump is seeing declining popularity as he approaches 100 days of his second White House term.

Opinion polls have shown Americans voicing concern over the billionaire's handling of key issues, including the cost of living, as well as his chaotic tariff policies.

The 22nd Amendment of the US Constitution states that "No person shall be elected to the office of the President more than twice."

Trump, who also served as president from 2017 to 2021, has insisted he is "not joking" about a third term, saying last month there are "methods" that would allow it to happen.

Any serious effort to amend the founding document would send the US into uncharted territory.

Changing the US Constitution to allow a third presidential term would require a two-thirds majority in both the House of Representatives and the Senate.

An amendment would also need ratification by at least 38 of the 50 US states, another slim possibility.