President Donald Trump’s Syria retreat marks a stark break from the interventionist philosophy that’s typified GOP foreign policy since the 9/11 terror attacks. This is precisely why Republicans in Congress have slammed Trump over the move, offering perhaps their loudest and most forceful criticism of the president yet.Trump’s decision to withdraw US troops from northeast Syria is a pivot into a broader retreat that Republicans have been pushing against for months. President Donald Trump’s decision to abandon the Kurds in Syria to a potential massacre at the hands of the Turkish military is a stark break from the brand of foreign policy the GOP has championed in era following the September 11 terror attacks. This explains why establishment Republicans, including some of Trump’s closest allies in Congress, excoriated the president over his abrupt move in what was perhaps the most forceful and widespread critique of the president from GOP lawmakers yet — and comes as he faces an impeachment inquiry.Republican Sen. Lindsey Graham, who typically acts as one of Trump’s staunchest defenders and sits on the Senate Foreign Relations Committee, said Trump’s decision “virtually reassures the reemergence of ISIS” and “makes it difficult for the US to recruit allies against radical Islam.”Sen. Rand Paul, among the few Republicans on Trump’s side in this move, has never been on the same page as other members of the party when it comes to foreign policy. In short, Paul is almost always an outlier on such matters. Trump and Republicans have consistently been at odds on how to fight terrorism.Since 9/11, Republicans have been staunchly interventionist when it comes to combatting terrorism and generally hawkish about America’s role in the world. They have at times disagreed on tactics or practices in this regard, such as the late Sen. John McCain speaking out against the use of torture, which the CIA called enhanced interrogation techniques, but they’ve been consistent in caution against the US pulling back from the world. Trump, with his isolationist “America First” philosophy, has posed a major challenge to this mainstream Republican worldview.He campaigned on pulling the US out of endless wars, and had no qualms about slamming President George W. Bush for the disastrous consequences of the 2003 invasion of Iraq. But as president he encountered a reality that made it difficult to deliver on those promises, with complicated situations on the ground in both Afghanistan and Iraq/Syria as well as GOP lawmakers pressing him against any abrupt withdrawals. Read more: Republicans and former US officials rip into Trump for abandoning the Kurds in SyriaWhen Trump announced he would withdraw all troops from Syria in late December, it prompted immediate uproar among congressional Republicans and led James Mattis to resign as secretary of defense. Seeking to quell the backlash, the president pumped the brakes on the withdrawal, and the US has maintained a force of around 1,000 troops in Syria. GOP lawmakers have largely avoided rebuking Trump over the slew of scandals that have swirled around his administration, including the latest one involving Ukraine, but they have never been louder in dissent than when the president breaks from the post-9/11 world order. Trump’s decision to withdraw troops from northeastern Syria is a victory for Syrian President Bashar al-Assad and therefore Russia and Iran. It also all but assures that ISIS prisoners, foreign fighters from Europe, will escape as the Kurds seek to counter a Turkish military operation. Not to mention, it sends a dangerous message to US allies that Washington does not have their backs and will abandon them regardless of how much they’ve sacrificed or promises made. The Kurds played a vital role in crushing ISIS’s caliphate, and the US is now leaving them to be decimated by Turkey. Trump’s Syria decision is a sign of a broader retreat on the horizon.There are essentially no visible benefits to this decision for the US, which explains why Democratic lawmakers in Congress — such as Sen. Chris Murphy — who tend to push for a more progressive foreign policy characterized by less interventionism and don’t necessarily think the US should maintain a longterm presence in Syria, are also rebuking the move. But the decision to pull troops from northern Syria and abandon the Kurds is also a pivot into the broader retreat Trump has long desired and pushed for, and this is why Republicans have been so vocal in their opposition.After the Syria decision was announced, Trump justified it by characterizing ISIS as a problem that’s “7,000 miles away” and far from the direct concerns of the US. Republicans in Congress vehemently disagree. Though the White House has pushed against the notion this move marks a withdrawal, and has characterized it more a relocation of certain troops to ensure they’re not caught in the cross fire of a Turkish-Kurdish fight, key Republicans have explicitly used such terminology. Republican Senate Majority Leader Mitch McConnell, for example, warned against a “precipitous withdrawal” of US troops from Syria. This is emblematic of what Republicans fear this development signals is to come in the future under Trump regarding the US presence in the Muslim world. The Trump administration announced the withdrawal of US troops from northeast Syria almost exactly 18 years after the beginning of the Afghanistan War, a conflict the president also wants to get out of. The US has maintained a consistent military presence in the Middle East, primarily as a result of policies first passed under a Republican president, for nearly two decades as part of the so-called war on terror. With the Syria retreat, Trump exhibited his willingness to go against the grain and break from this prolonged, GOP-initiated military occupation — even if it does not benefit the US or its allies and without a broader plan in place. Trump has stayed the course with traditional Republicanism on a wide array of issues, but with foreign policy he’s a complete wild card — and that’s why it’s the one issue where members of his own party will actually stand against him.