President Trump’s economic adviser said Sunday the administration will be tougher on spending as the budget deficit is projected to hit $1 trillion.

Larry Kudlow, director of the National Economic Council, told CNN that the lower taxes following the GOP tax cuts will yield lower revenue at first, but he believes the corporate tax cut will be paid for by 2020.

“I reckon it will take us a year, maybe 18 months to turn that around,” Mr. Kudlow said. “We are going to be tougher and tougher on spending.”

Mr. Kudlow said faster economic growth and getting strict on spending will eventually decrease the deficit.

His comments come as Congress is running up against a deadline to fund the government by the end of September.

Recent reports suggest the looming deadline may present the president with another large omnibus spending bill, which Mr. Trump said he would refuse to sign.

In March, the president signed a $1.3 trillion spending bill, the second-largest in history.

“I say to Congress: I will never sign another bill like this again,” Mr. Trump said earlier this year. “It became so big because we need to take care of our military, and because the Democrats, who don’t believe in that, added things that they wanted in order to get their votes.”

He called on Congress at that time to grant him a line-item veto to cut out certain spending items. Lawmakers, though, have not given him that power.

In a tweet Sunday morning, the president suggested he would support a government shutdown if he doesn’t get money to secure the southern border.

“I would be willing to ‘shut down’ government if the Democrats do not give us the votes for Border Security, which includes the Wall! Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our Country!” Mr. Trump tweeted.

The Senate’s bill would fund the Department of Homeland Security with $1.6 billion for the wall, while the House bill includes $5 billion for the wall, according to The Hill.

Over the weekend, Senate Majority Leader Mitch McConnell, Kentucky Republican, told 840 WHAS radio that funding for Mr. Trump’s border wall would likely come after the midterms.

The president also took to Twitter on Sunday morning to celebrate the more than 4 percent economic growth.

“The biggest and best results coming out of the good GDP report was that the quarterly Trade Deficit has been reduced by $52 Billion and, of course, the historically low unemployment numbers, especially for African Americans, Hispanics, Asians and Women,” Mr. Trump tweeted.

• Dave Boyer contributed to this article.