Evangelical Christian leaders criticized President Donald Trump's decision to withdraw US forces from northern Syria, exposing the US' Kurdish and Christian allies to an attack by Turkey.

The leaders, including Franklin Graham, argue that Christians living in the region will now be vulnerable to a Turkish attack.

Christian right leader Pat Robertson said Trump "is in danger of losing the mandate of heaven," and evangelical radio host Erick Erickson called to speed up Trump's impeachment.

Support from evangelical Christians is key to Trump's chances of victory in 2020. Eighty percent of evangelicals voted for Trump in 2016.

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Evangelical Christian leaders have criticized President Donald Trump's decision to withdraw US forces from Syria, in a move likely to threaten his support base in the 2020 presidential election.

The evangelical community is among Trump's strongest bases of support, and a key part of the coalition that allowed him to win the presidency, with 80% of evangelical Christians voting for Trump in 2016.

But this week, evangelical leaders argued that Trump's withdrawal — which allows Turkey to attack the US's Kurdish allies in the region — could endanger Christians.

They added that Christians who fight alongside the Kurds would be vulnerable to attack, and Christian communities in the Muslim-dominated region — who are free to worship — would be endangered.

At least 16 Kurdish fighters have died, according to the Syrian Observatory for Human Rights, within the first day of Turkey's military operation in Syria. There have been no reports so far about Christian deaths.

They also said the US withdrawal would embolden Iran, a key ally of Syrian President Bashar al-Assad and an enemy of Israel.

Syrians flee shelling by Turkish forces in Ras al Ayn, northeast Syria, on October 9, 2019. Associated Press

'The President of the United States is in danger of losing the mandate of heaven'

Franklin Graham, the son of evangelical leader Billy Graham, tweeted on Wednesday: "TODAY I ask that you join me in praying for the lives affected by the White House decision to pull U.S. troops out of northern Syria. Both Democrat & Republican leaders are deeply concerned bc this would be, in essence, abandoning our closest allies there — the Kurdish people."

"Also pray for the Christians who the Kurds have been protecting. They could be annihilated," he added. "Would you pray w/me that Pres. @realDonaldTrump will reconsider? Thousands of lives hang in the balance."

Read more: Trump defends abandoning the Kurds by saying they didn't help the US in WWII

Trump with Franklin Graham. Ralph Freso / Stringer / Getty Images

Similarly, Christian right leader Pat Robertson told his TV show on The Christian Broadcasting Network, "The 700 Network," on Monday: "I believe ... the President of the United States is in danger of losing the mandate of heaven if he permits this to happen."

Robertson added that he was "appalled" by Trump's decision to pull out of Syria, and claimed Trump "is now allowing the Christians and the Kurds to be massacred by the Turks."

Erick Erickson, an evangelical radio host, also suggested fast-tracking Trump's impeachment over the Syria withdrawal.

"Hey @SpeakerPelosi, maybe do a vote to initiate impeachment STAT, have the committee get out articles by tonight and over to the Senate, and perhaps we'll still have time to save some of the Kurds," he tweeted on Wednesday.

The Democrat-led House is currently pursuing an impeachment inquiry into Trump after a whistleblower complaint revealed that he had asked Ukraine's president to investigate Democratic rival Joe Biden and his son.

Rep. Lindsey Graham, a prominent Trump ally who has criticized the president's decision to withdraw from northern Syria. Alex Brandon/AP

Trump's withdrawal from the US has alienated some of his closest congressional allies as well.

Sen. Lindsey Graham, one of the president's biggest supporters, tweeted on Wednesday that the Trump administration had "shamelessly abandoned" the US' Kurdish allies, and that the move "ensures the reemergence of ISIS."

Read more: Lindsey Graham threatens 'sanctions from hell' and warns Turkey against crossing a 'red line' as it readies for attack in Syria

Trump can't afford to lose the evangelical vote

The chorus of criticism from these traditional allies comes as Trump can ill afford to lose their backing amid the impeachment inquiry.

A recent Fox News poll found that 28% of white evangelicals now support Trump's impeachment, a 5% increase on July's percentage and higher than other core areas of Trump's vote.

However, Christian Broadcasting Network political correspondent David Brody said the evangelical vote could still prove resilient and that evangelicals could still back Trump despite Syria.

He told The Washington Post that the backlash over Syria amounts to "a mini crisis" for the White House, but added: "The president has done so much for evangelicals, in terms of judges and legislation, that this Syria decision isn't going to be the death knell."

In a show of support, Faith and Freedom Coalition founder and prominent Trump supporter Ralph Reedargued in book excerpts published on Wednesday that evangelicals have a "moral obligation" to back Trump in 2020.

According to Defense One, he told reporters on Wednesday that Turkey had committed to protecting the rights of minorities in northern Syria, including those of Christians, and said it would face economic sanctions if it failed to comply.