House Democrats are preparing an ambitious 100-days agenda focused on delivering their campaign promises - making life more affordable and conducting vast oversight of the Trump administration - if the party seizes majority control in next month's elections.

Democratic leader Hakeem Jeffries, who is in line to become House speaker if the party wins power, said the Democrats will be united "right out of the gate" on reinstating Affordable Care Act tax breaks, reversing Republican Medicaid cuts, holding votes against the Iran war and undoing President Donald Trump's tariff regime.

They expect to launch the agenda in the first 100 hours, once the new Congress is seated in January.