United States President Donald Trump has announced he plans to spend more than $400m to help Republican candidates win the November 3 midterm elections as his party fights to maintain its grip on Congress.

In a post on his Truth Social platform on Tuesday, Trump wrote that much of that total had already been spent on campaign outreach.

“More than 300 Million Dollars has already been spent on Advertising, Direct and Indirect Voter Contact, Rallies, Rally Arenas, Telerallies, Get Out the Vote Programs, Election Integrity, and more,” Trump said.

“It is my Great Honor to do so on behalf of the Republican Party, which has done so much to bring our Country back from the Edge of Oblivion.”

He added that the November vote was “the Most Important Midterm Elections in our Country’s History”.

The president offered no detailed breakdown of the spending, including how much would reach individual races.

But the promised influx of spending comes as Trump’s Republican Party faces headwinds ahead of the election, including pushback over the economy and the protracted US-Israeli war against Iran.

In the lead-up to the vote, Trump’s approval ratings have tumbled to record lows. A poll this week from the news agency Reuters and the research firm Ipsos found that only 31 percent of Americans approved of Trump’s job performance so far.

Some Republicans have sought to distance themselves from the president as a result. Others have pushed for greater support, particularly for close races with Democrats.

Questions have swirled over whether Trump and his allies would tap into the war chest amassed by MAGA Inc, the super PAC named for his “Make America Great Again” movement.

As a super PAC — or political action committee — MAGA Inc can raise unlimited sums from donors to support or oppose federal candidates. But its spending is legally required to remain independent of their campaigns.

Last month, the Campaign Legal Center (CLC), a campaign finance watchdog, accused Trump of violating those rules by claiming control over MAGA Inc’s expenditures.

The group cited the president’s public statements, including an exchange with reporters in the Oval Office on September 4, when Trump was asked when the money would start flowing to Republican candidates.

He replied that he would spend “whatever amount of money necessary” to help his party. He then added: “This is money from MAGA Inc. This is my money that I control.”

According to its latest federal filing, MAGA Inc entered September with $415.8m in cash reserves, making it one of the most consequential financial resources in the Republican campaign arsenal.

But Trump has questioned why the super PAC’s hefty outlay has not improved Republican polling in key races, including in Ohio, according to Reuters.

Other Trump-aligned groups have also ramped up their political advertising, including two newly formed organisations linked to MAGA Inc, the No Going Back PAC and the Safety and Affordability PAC.

The advertisement tracker AdImpact found that the No Going Back PAC contributed $68.7m in political ads last month alone.

Another Trump ally, tech entrepreneur Elon Musk, has reportedly spent $366m since last year on Republican campaigns through his group, America PAC, and other Republican and conservative groups.

In the final weeks of the midterms, Trump himself has hit the campaign trail, forging ahead with a 32-day campaign blitz. Upcoming stops include South Carolina and Iowa.

The stakes of this year’s election are considerable. Control of Congress hangs in the balance.

Currently, the Republican Party holds slim majorities in both legislative chambers, but Democrats are seeking to leverage Trump’s declining popularity to flip the Senate and the House of Representatives.

If they are successful, they could stymie Trump’s legislative agenda for the final two years of his presidency.