WASHINGTON (Reuters) - As U.S. President Donald Trump intensifies his efforts to brand four progressive congresswomen as the new face of the Democratic Party, its presidential front-runner, Joe Biden, has been quietly reminding voters in Iowa there remains a middle ground.

FILE PHOTO: Democratic 2020 U.S. presidential candidate and former U.S. Vice President Joe Biden speaks at a campaign stop at Mack's Apples in Londonderry, New Hampshire, U.S., July 13, 2019. REUTERS/Brian Snyder

Trump’s vilification of Alexandria Ocasio-Cortez, Ilhan Omar, Ayanna Pressley and Rashida Tlaib, in which he said the minority lawmakers were hostile to America and should “go back” where they came from, has largely left Biden out of this week’s political conversation.

But it may give Biden’s campaign the boost it needs after his widely panned debate performance last month.

Biden, who served eight years as Barack Obama’s vice president and 36 years as a U.S. senator, epitomizes a Democratic establishment the four congresswomen who dub themselves “the squad” have vowed to upend.

Ocasio-Cortez, 29, has at times been a fierce critic of Biden, knocking him as being politically out of touch and suggesting he may be too old to be president.

Biden, 76, has had to be careful in criticizing them in return, not wanting to alienate the party’s emboldened activist left whose votes he will need if he wins the Democratic nomination to face Trump in the November 2020 election.

At the same time, he is working to make clear to moderate voters that he would be a more palatable alternative than a Democratic nominee more in line with the congresswomen’s values, such as U.S. Senator Bernie Sanders.

The approach has seen Biden condemning Trump’s attacks on the congresswomen as racist, another sign the Republican president is “tearing the soul out of this country,” Biden said on Wednesday in Council Bluffs, Iowa.

But he also indicated he did not believe the four represented the mainstream of the Democratic Party.

In an interview with MSNBC this week, Biden expressed his support for House Speaker Nancy Pelosi in her struggle with the four to maintain a united policy front in the House of Representatives.

Biden noted that the large majority of seats won by House Democrats in last year’s congressional elections were secured by moderates in his own mold, not self-described socialists such as Ocasio-Cortez.

Voters who support Biden have told Reuters they are concerned the party is drifting too far leftward to beat Trump next year.

Biden spent much of the week defending his healthcare plan - which would bolster the Affordable Care Act, popularly known as Obamacare, and let consumers keep their private insurance plans - against attacks by Sanders, who favors a government-run system.

In that dispute, Biden defined himself as what he calls an “Obama Democrat,” one who wants to preserve the former president’s signature healthcare achievement, rather than “start over with something new.”

“Biden’s theory of change is change as a restoration of stability,” said Scott Kozar, a Democratic strategist who was involved in the 2018 congressional elections.

‘PERFECT PLACEHOLDER’

Trump’s campaign advisers have long sought to paint the entire Democratic presidential field as “socialists.”

They believe they were aided in that effort in last month’s Democratic debate when several candidates on stage came out in favor of eliminating private health insurance, and a larger number supported providing healthcare for immigrants in the country illegally, and decriminalizing the unauthorized crossing of the U.S. border.

When Trump decided earlier this week to exploit the rift between Pelosi and Ocasio-Cortez’s group, his campaign saw a way to use his tweets in its narrative that the four had become the new standard-bearers for the party, said Ford O’Connell, a Republican who works with the campaign on strategy and messaging.

The squad “is the perfect placeholder until you have a nominee,” O’Connell said.

On Thursday, Trump’s campaign was more overt in its intention. “The Squad, as they call themselves, are now the leaders of the Democrat Party,” the campaign’s communications director, Tim Murtaugh, said in a statement.

Kozar suggested Trump may end up going too far, giving someone like Biden an opportunity to “triangulate” the race by appealing to voters turned off both by Trump’s conduct and the progressive left.

In his MSNBC interview, Biden appeared to try to walk back some of the positions he took at the debate, particularly on immigration, saying he believed immigrants who are in the United States illegally merited healthcare services only in emergencies and that border crossing should not be completely decriminalized.

“What I’m saying is, you still should not be able to just cross the border,” Biden said. “You’ve got to get in line.”

Matt Bennett, executive vice president of Third Way, a centrist Democratic think tank, said there was a danger the party could play into Trump’s hands unless a moderate such as Biden pushes back at the president’s attempts to frame the election as a contest between himself and a dangerous leftist.

“It’s a lot easier to make that stick if you lean into it,” Bennett said.