President Donald Trump has too many 2020 Democratic candidates to choose from, so he's focusing his early campaign attacks on "the Squad."

"The Squad" is the nickname for four progressive lawmakers whom Trump recently attacked in racist tweets: Reps. Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota, Rashida Tlaib of Michigan, and Ayanna Pressley of Massachusetts.

The freshman Democrats have emerged as primary targets of conservative media and Republicans, who are painting them as the new face of the Democratic party.

Roughly a month after targeting "the Squad" with racist tweets, Trump on Thursday urged Israel to bar Omar and Tlaib from entering the country.

"It would show great weakness if Israel allowed Rep. Omar and Rep. Tlaib to visit. They hate Israel & all Jewish people, & there is nothing that can be said or done to change their minds," Trump tweeted

As a key part of his 2020 campaign strategy, Trump is looking to exploit conservative disdain for these lawmakers as well as Democratic divisions as he works to smear the party as overrun by extremists.

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President Donald Trump's default mode is to attack those he perceives as his opponents, and therefore seems to operate best when he has a clear target in mind.

In 2016, it was former Secretary of State Hillary Clinton. Ahead of the 2018 midterms, it was House Speaker Nancy Pelosi.

With over 20 candidates trying to elbow their way toward the 2020 Democratic presidential nomination, it's a bit difficult for Trump to zero in on a single person until the field is whittled down.

But Trump has found the perfect substitute, a group that checks off all of the boxes when it comes to riling up his base: Democratic Reps. Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota, Rashida Tlaib of Michigan, and Ayanna Pressley of Massachusetts.

The four progressive lawmakers, who've become known as "the Squad" on Capitol Hill, are among the most left-leaning members of Congress. All are women of color, two are Muslim, and one was formerly a Somalian refugee before becoming a US citizen as a teenager.

Trump is trying to use 'the Squad' to divide Democrats and rile up his base

These four women arguably present the biggest challenge to the status quo in Washington at present.

Simply by getting elected in the 2018 midterms, they all made history: Ocasio-Cortez as the youngest woman to be elected to Congress, Pressley as Massachusetts' first female black member of Congress, and Tlaib and Omar as the first two Muslim women to ever serve in Congress.

Read more: Here's the difference between a 'socialist' and a 'Democratic socialist'

And on top of unabashedly criticizing the president, these lawmakers are unapologetically public about where they stand on the issues — even if it means opposing and criticizing Democratic leadership. Their propensity for going against the grain has made them routine targets of conservative media, and last month their differences with House Speaker Nancy Pelosi spiraled into a highly publicized, contentious intraparty battle.

In an apparent effort to exploit this, Trump in July attacked "the Squad" in a series of racist tweets suggesting that they "go back" and "help fix the totally broken and crime infested" countries "from which they came."

All four lawmakers are US citizens, with only Omar among them born outside the US. Trump's tweets played off of the racist "go back to Africa" trope and ignited a firestorm of criticism.

But Trump in the weeks since has continued his onslaught of criticism against "the Squad," and rejected the notion his tweets were racist. He said he doesn't have a "racist bone" in his body.

'SEND HER BACK!' was just the beginning

In perhaps the ugliest moment yet in this racism-fueled saga, Trump supporters chanted "SEND HER BACK!" as the president attacked Omar at a rally in Greenville, North Carolina, in mid-July. It was a sign of what's to come along the campaign trail, with "send her back" replacing "lock her up" as the rallying cry of Trump's base.

And by attacking "the Squad" with xenophobic commentary and racist tweets, Trump is tapping into many of the same sentiments that helped him take down a huge field of Republican contenders in 2016.

The president in the 2016 campaign season made vilifying refugees and immigrants a central part of his strategy. Along the campaign trail, Trump described Mexican immigrants as "rapists" and "drug dealers," characterized Syrian refugees as a "great Trojan horse," and called for banning all Muslims from entering the US.

Read more: Weeks of Democratic infighting between Nancy Pelosi and 'the Squad' preceded Trump's racist tweet attacks

The president's attacks on a group of minority lawmakers with ties to the refugee, Muslim, and Latino communities build off of these sentiments. He's painting them as anti-American, misleadingly equating criticism of his administration with hatred of the US. In this vein, he's said that if "the Squad" isn't happy in the US, they can leave.

In the moments before Trump supporters began chanting "SEND HER BACK!" in North Carolina, the president said of Omar, "She looks down with contempt on the hard-working Americans, saying that ignorance is pervasive in many parts of this country."

A key part of Trump's campaign strategy thus far has also been to tie Democrats to socialism. He's trying to convince his base that the Democratic party has been overrun by left-wing extremists who want to turn the US into Venezuela. Ocasio-Cortez, a self-declared democratic socialist, offers a prime opportunity to continue this hyperbolic narrative.

"The Dems were trying to distance themselves from the four 'progressives,' but now they are forced to embrace them. That means they are endorsing Socialism," Trump said in a tweet last month.

Echoing this theme at his Greenville rally, Trump said, "Tonight, we renew our resolve that America will never be a socialist country. A vote for any Democrat in 2020 is a vote for the rise of radical socialism and the destruction of the American Dream — frankly, the destruction of our country."

Additionally, Trump has zeroed in on Omar's criticism of US support for Israel as a point of attack.

Omar earlier this year was accused of anti-Semitism over her critique of the relationship some US lawmakers have with the Israeli government. Though she apologized and maintained that she did not intend to offend the Jewish community, Trump has continued to hammer the Minnesota lawmaker on this issue.

Roughly a month after targeting "the Squad" with racist tweets, Trump on Thursday urged Israel to bar Omar and Tlaib from entering the country.

"It would show great weakness if Israel allowed Rep. Omar and Rep. Tlaib to visit. They hate Israel & all Jewish people, & there is nothing that can be said or done to change their minds," Trump tweeted.

Not long after the president's tweet, the Israeli government announced it would not allow the lawmakers to visit. The move unleashed a slew of criticism — including from the powerful pro-Israel lobby. Responding to this development, Ocasio-Cortez in a tweet said Trump is "exporting his bigotry & making matters worse."

Trump might be right that 'many people' agree with him

Until the field of Democratic candidates is narrowed down, which likely won't occur in a significant way until the Iowa caucuses in February 2020, these attacks on "the Squad" are poised to continue. In the process, Trump's refrain to his supporters will be that Democrats are un-American, socialist, and anti-Semitic.

This tactic could drive voters on the fence away from Trump, particularly in communities of color, but there are also signs that Republicans will become further enamored of the president along the way. A poll conducted after Trump's racist tweets, for example, found Republican approval of Trump went up.

In one of his many defenses of his tweets last month, Trump said he wasn't concerned they were being labeled racist or emboldening white nationalist groups because "many people agree with me."

Based on the evidence we've seen so far, he might be right.