Donald Trump’s signature policy issue during his campaign was forcing unauthorized immigrants out of the United States. But it would be a mistake for Republicans in Congress to fund any effort to make this dream a reality during his administration. Trump won the presidency, but he failed to convince anyone, including Republicans, on the issue that he spent the most time promoting, and history still shows that an anti-immigration agenda could become incredibly damaging to the GOP's electoral prospects long-term.

Here are six reasons why congressional Republicans shouldn’t confuse a Hillary Clinton loss with a mandate to target immigrants.

1. The vast majority of voters still want to let the immigrants stay. A supermajority of Americans favors legalizing immigrants who are in the country illegally, according to exit polls from CNN (70%), Fox News (70%), the New York Times (70%), ABC News (71%), CBS News (70%), and the Wall Street Journal (71%). In fact, even more Trump voters favored legalization than favored deportation. This jives with Pew Research Center’s most recent poll that found that fully two-thirds of Republicans favored legal status for unauthorized immigrants. As the figure below shows, Trump failed to persuade Americans during his campaign despite making it his number one talking point. It would be foolish for the GOP to think that this will suddenly change.

Figure: Should undocumented immigrants be allowed to stay in the United States?

Sources: Pew (October 2014–March 2015); Wall Street Journal (November 2016)

2. GOP senators in close races who favored legalization performed better than Trump in their states. Trump’s immigration position did little, if anything, to advance his cause in the swing states. All of the incumbent Republicans who supported legalization in tight Senate races—Senators John McCain (AZ), Marco Rubio (FL), Mark Kirk (IL), Kelly Ayotte (NH), Rob Portman (OH), and Ron Johnson (WI)--outperformed Trump in their states. Sens. Richard Burr (NC) and Pat Toomey (PA) who tried their best to avoid discussing the subject while not supporting Trump’s deportation position netted the same share of the vote as Trump. Sen. Roy Blunt disavowed a path to legal status and did worse than Trump in Missouri.

3. Many Republicans in the House and Senate don’t agree with Trump. Well over a hundred GOP senators and congressmen have publicly backed legal status for unauthorized immigrants in the United States (here are some). Trump will need to lead a party that includes these members. Party leaders in Congress would be unwise to abandon such members now that they have helped the GOP achieve a majority. Ironically, the fact that Hillary Clinton did so poorly, with low voter turnout hurting Democrats in competitive races, actually helped to maintain this moderate wing of the Republican Party. The GOP would likely be in a worse position to support real immigration reform if the election had been a Democratic blowout.

4. California Republicans won on nativism in the 1990s—and it cost them everything. The Republicans made blaming unauthorized immigrants for crime and government deficits a major part of their campaign in 1994. Governor Pete Wilson championed a ballot measure, Prop. 187, intended to expel the state’s undocumented immigrants. The measure actually had the support of a majority of voters, but as my colleague Alex Nowrasteh has meticulously documented, the campaign turned California permanently blue. Wilson had an electoral mandate in 1994, and the Republicans still lost the state for a generation. Trump has no such mandate today.

5. Trump won a single election, but deportations could lose a generation of voters. One reason why misinterpreting Trump’s victory could be devastating for the GOP in the long-term is that barely any young people agree with him. Only 17 percent of Americans under 30 agree that unauthorized immigrants “should not be allowed to stay,” according to the latest survey from the Pew Research Center, and only 37 percent of these voters backed Trump. Republicans will still need a pro-immigrant strategy to address this issue.

6. Trump is the most unpopular president-elect ever. It is impossible to overstate the importance of this point. Americans have never elected a person that they find so disagreeable. Fully 61 percent of voters said yesterday that they had an unfavorable view of Trump. It makes little sense for Republicans to try to help the new president build goodwill by doing something that the vast majority of Americans do not want.

These political calculations all stand in addition to the multitude of economic and moral reasons to oppose removing from the country people who have built their lives in the United States.