Cranky conservatives are already complaining about the proposed border wall deal. They shouldn’t be. Both they and President Trump should take the deal and move on to fight another day.

We don’t have all the details yet, but it appears Trump will get $1.375 billion to build an extra 55 miles of border fencing. That’s only a quarter of the $5.7 billion he had asked for, and leaves the country well short of what it needs to secure the southern border. It’s easy to see why conservatives are upset.

But — news flash — that’s the best they are going to get with Democrats in control of the House. Elections have consequences, as Democrats forced to deal with Trump on the border are painfully aware. That works both ways, though. Americans have voted for divided government (again), and that means both sides must compromise.

The alternative to the deal is another government shutdown, something no sentient conservative should want. Government shutdowns are always unpopular because the people rightly think they should not be punished because their leaders can’t work together. Trump’s job approval ratings predictably declined during the most recent shutdown and have only started to recover. Forcing a second shutdown over the wall will likely create deeper, and more lasting, political damage.

There’s also the political reality that the public does not want the wall, at least right now. No poll shows that a majority of voters support Trump’s vision. Forcing an unpopular shutdown over an unpopular wall is stupid politics.

Trump could always sign the deal and then try to get funds for the wall by other means, either through an emergency declaration or by transferring already-appropriated funds from other government accounts. But while that would delight many conservatives, it would be a bad move.

Any executive order to do this would almost certainly be challenged in court and would have the further disadvantage of keeping the focus on a losing issue. The singer Kenny Rogers crooned that a gambler needs to “know when to hold ’em, know when to fold ’em.” For now, folding via the deal is the best option on the table.

Trump and the GOP need to improve their chances of winning in 2020 before trying for something so sweeping. A president with a 42 percent job approval rating, as the most recent RealClearPolitics average shows, is not in a position to dictate outcomes. Democrats know this and would love to keep him on the ropes, as a refusal to take the deal would do.

Taking the deal allows the president to move on to stronger political ground. His negotiations with North Korea and China are at a critical stage. Successful outcomes in one or both will likely redound to his benefit. The economy continues to roar; moving the discussion from the wall to the wallet is also good for the GOP. Fighting on ground that’s winnable is always a better move.

Fighting to the last on a purported matter of principle nonetheless seems to be baked into some conservatives’ DNA. President Ronald Reagan faced conservative revolts a number of times, especially when he twice proposed raising taxes in 1982 and when he made a landmark deal on Social Security with Democratic House Speaker Tip O’Neill (Mass.). In each case, the Gipper plowed ahead with the deal, creating a bipartisan coalition to work his will.

Reagan did this because he distinguished principle from ideology. The principled conservative would, as he said in his autobiography, “An American Life,” take what he could get “and fight for the rest later.” He strongly disagreed with those he called “radical conservatives” who “wanted all or nothing and they wanted it all at once." That sort of person, he argued, “jumps off the cliff with the flags flying” and inevitably loses everything.

Reagan knew not to hold the perfect as the enemy of the good, and that change comes slowly. As he wrote in December 1964, “Human nature resists change and goes over backward to avoid radical change.” Changing minds takes persistence and skill, but most of all it takes time.

Conservatives should give Trump, and themselves, the time needed to change minds about the wall and to improve their chances of winning in 2020. Quit complaining, take the deal and start winning.

Read more:

The Post’s View: Come on, lawmakers. Not another shutdown.

Greg Sargent: With new border deal, Republicans are trying to negotiate Trump’s surrender

Jennifer Rubin: Texans to Trump: Forget about the wall

Greg Sargent: Trump’s wall is a potent symbol. Not just for his supporters. For his opponents, too.

Ann Telnaes: Trump is changing his narrative on the wall