The single biggest pearl of Beltway conventional wisdom to suffer irreversible tarnish in 2017 was the notion that Donald Trump stood for an iconoclastic "populism" poised to redefine the dominant governing ideology of the Republican Party. Trump's past support for Democratic candidates and policies, his weak ties to conservative elites in Washington, and his infrequent rhetorical devotion to the American right's familiar themes of limited government, constitutional fealty, individual liberty, and traditionalist sexual ethics convinced many political analysts during the 2016 campaign that he represented a dramatic break from his adopted party's existing ideological legacy. Critics ranging across the political spectrum from National Review to Barack Obama reinforced the dominant news media judgment that Trump was not a regular conservative—and voters ultimately agreed, perceiving Trump as significantly closer to the ideological center than previous Republican presidential nominees.
But the existing Republican Party has exerted a strong gravitational pull on Trump, who seems to lack many personal substantive commitments and who does not command a larger faction of allies within the GOP dedicated to shifting its platform away from standard conservative positions. Indeed, Trump's record in office so far can be fairly described as the most consistently conservative of any president in modern history, as he has proven to be much less inclined than Richard Nixon, Gerald Ford, either George Bush, or even Ronald Reagan to pursue centrist or bipartisan initiatives in select policy domains.
And in at least one major area, it's Trump who's pushing other Republicans in a conservative direction rather than vice versa. The extensive attention devoted by the mainstream media to Trump's verbal departures from conservative doctrine on topics like trade, Medicare, and the Iraq War in 2016 somewhat obscured the fact that on his signature issue—immigration—Trump quite conspicuously ran to the ideological right of the rest of the Republican presidential field, to say nothing of the Democratic opposition.
While Candidate Trump's invocations of economic populism and military non-intervention have not often guided the policy positions of President Trump's administration, his commitment to reducing the number of immigrants residing in the United States has only deepened once in office. The Trump campaign mostly emphasized combating illegal immigration via more aggressive internal enforcement and a "big, beautiful wall" across the Mexican border, but the Trump presidency is also pursuing a significant cut in legal immigration rates and proposing reforms to the criteria governing the process of granting authorization to would-be residents. Attempts by congressional Democrats and a few breakaway Republicans to provide "DREAMers" with legal status in exchange for increased border security funds have now foundered in Congress due in large part to newfound presidential demands over the past few weeks that major reductions to lawful immigration also be included in the deal.
To be sure, the Republican Party as a whole has not yet openly embraced Trump's call for slashing legal immigration rates. Even some supporters of the Senate legislation endorsed by Trump are not publicly defending the very provisions in the bill that would implement such a policy, and business interests within the Republican Party network are unlikely to be satisfied (the U.S. Chamber of Commerce has already expressed its opposition). But the bulk of congressional Republicans, including top leaders in both chambers, have backed the Trump administration's proposal to resolve the DACA issue by rolling it into a larger reform bill that would otherwise shift immigration policy in a more restrictive direction on the legal and illegal fronts alike, while opposing the narrower DREAMers-for-security-dollars swap negotiated by a bipartisan Senate group.
There are political risks to the Trump approach. Previous Republican presidents departed from ideological purity because they also prized racking up legislative achievements and appealing to voters beyond their party base. Trump is making a very different bet—though not necessarily an incorrect one—that holding to a tough line on immigration will either compel Democrats to make further concessions or keep an issue alive that works to his electoral advantage even if he can't (accurately) claim progress in constructing his famous border wall. The pragmatic, deal-making, I-can-fix-it Trump we heard so much about during the 2016 campaign still makes occasional appearances for the benefit of the cameras; only last month this Trump publicly told Congress he'd sign any bipartisan agreement on DACA and "take the heat" from his supporters for doing so. But the Trump who actually governs, the Trump who shot down the bipartisan agreement with which he was then presented in a fusillade of anger, is best understood as the increasingly ideological leader of an increasingly ideological party.