WASHINGTON — Sen. Chuck Schumer, in line to be the Senate minority leader, will work with Republicans on infrastructure spending and ethics reform, but will fight any attempts to repeal the Affordable Care Act or Wall Street reforms, his allies said last week.

By focusing on rebuilding infrastructure, which could create jobs, as well as curbs on lobbyists and campaign finance, which could address voter anger at Washington, the New York Democrat hopes to make common cause with Republicans while also mending ideological splits in his own party, they say.

Yet Schumer, his allies said, is like everyone else in this town: He can only guess what kind of president Donald Trump will be after the 70-year-old businessman turned Washington upside down by winning an unexpected victory on Tuesday.

“Everybody is keeping their powder dry right now,” said Danielle Pletka, a senior vice president at the American Enterprise Institute, a conservative think tank. “There is a serious question among Democrats and Republicans about how Donald Trump is going to govern.”

That makes Schumer’s new role as top Democrat in the Republican-controlled Congress more unpredictable than usual.

Schumer has kept a low profile since Trump won, pondering the election results and consulting with colleagues about the next steps his party should take.

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He declined to discuss his thinking about the role he will play as the leader of the Senate opposition.

Senate Majority Leader Mitch McConnell (R-Ky.) and House Speaker Paul Ryan (R-Wis.) said last week they want to hit the ground running with their conservative agenda, which would strip many of President Barack Obama’s legislative achievements.

One of their top priorities is to repeal what they call Obamacare. Democrats say they will agree to fix it but not to scrap it. Schumer probably will force Republicans to pass major changes with 60 votes (Republicans hold 51 seats), though they can undo its tax and budget provisions with 51 by using a parliamentary procedure.

Schumer also will have to devise a strategy for opposing Republican plans to strike down Wall Street regulations such as the Dodd Frank Act, to lower corporate tax rates and to derail international agreements on climate change, allies say.

And Schumer and Democrats will probably fight confirmation of a conservative nominee to the Supreme Court’s open seat, which McConnell refused to fill with Obama’s selection. But if Schumer blocks Trump’s choice, McConnell could respond by ending filibusters on high court appointments.

Schumer will begin to make his plans clear this week, when Congress ends its recess on Monday to work on a few priorities, especially approving a spending bill to keep the federal government open past Dec. 9.

When Senate Democrats meet Wednesday to select their leaders for the next Congress, Schumer is expected to be a shoo-in for Senate minority leader.

In his new role, Schumer will not only have to negotiate with McConnell on the Senate’s daily agenda for legislation brought to the Senate floor, but he will also have to manage a 48-member Democratic caucus that spans the spectrum, according to University of Maryland government professor Frances Lee and Rep. Steve Israel (D-Huntington).

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After a devastating loss on Tuesday, Democrats are in a virtual war over their future direction, with activist Adam Green and other populists on the left calling for a “full reckoning” and rejection of the “rigged economy.”

Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts are publicly trying to pull the party to the left, but a half dozen moderates up for re-election in 2018, such as West Virginia’s Sen. Joe Manchin, are calling for a more moderate course.

That will be a major challenge for Schumer, who will attempt to hold his party together though his use of committee assignments, jawboning and legislative priorities both sides can support and that can win over Trump voters.

For the past three years, Schumer has worked hard to build a reputation on both sides of the aisle as someone that Republicans could work with and as a willing and accomplished political deal-maker.

Schumer will create a better working relationship with McConnell than the combative, and retiring, Senate Minority Leader Harry Reid (D-Nev.) has had.

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And Schumer, the deal-maker from Brooklyn, will test whether he can work with fellow New Yorker Trump, the negotiator from Manhattan via Queens, an acquaintance who has donated to his campaign.

“What Schumer is not going to do is to make the declaration that Mitch McConnell made when Barack Obama became president — that his goal is to make Trump a one-term president,” said spokesman Matt Bennett of Third Way, a moderate Democratic think tank.

“If Trump comes to the table with some reasonable proposals, Chuck Schumer is going to be all ears. If he comes with something that is offensive, then he’s going to fight and he’s going to fight hard,” Bennett said.

Rep. Peter King (R-Seaford), who knows both Schumer and Trump, said, “Chuck realizes he has at least four years dealing with a Republican president. I would say the odds are they can find common ground.”

But, he added, “Like New Yorkers, they’ll probably have some hot and cold moments.”