WASHINGTON — President Trump will seek $8.6 billion in his new budget to build the U.S.-Mexico border wall, two administration officials said Sunday, setting up another showdown with Congress, which has resisted giving him more money for his signature campaign promise.

The request would more than double the $8.1 billion already available to the president after he declared a national emergency at the border in order to circumvent Congress once lawmakers refused his funding demands. That standoff led to a 35-day partial government shutdown, the longest in U.S. history.

The officials confirmed that the request was part of Trump’s spending blueprint for the 2020 budget year that begins Oct. 1. That document, which sets the stage for negotiations ahead, proposes boosting to defense spending to $750 billion while reducing nondefense accounts by 5 percent, with cuts recommended to safety net programs used by many Americans. The plan sticks to budget caps that both parties have routinely broken in recent years and promises to come into balance in 15 years, relying in part on economic growth that may be uncertain.

The officials were not authorized to publicly discuss budget details before Monday’s release of the plan and spoke on condition of anonymity.

White House economic adviser Larry Kudlow said Trump’s budget “points a steady glide path” toward lower spending and borrowing as a share of the nation’s economy. He also told “Fox News Sunday” that there was no reason to “obsess” about deficits, and expressed confidence that economic growth would top 3 percent in 2019 and beyond. Others have predicted lower growth.

Budget proposals are merely a starting point, but leading Democrats immediately rejected this request.

“Congress refused to fund his wall and he was forced to admit defeat and reopen the government. The same thing will repeat itself if he tries this again,” said House Speaker Nancy Pelosi, D-Calif., and Senate Democratic leader Chuck Schumer of New York. They said the money “would be better spent on rebuilding America.”

The budget arrives as the Senate readies to vote this week to terminate Trump’s national emergency declaration. The Democratic-led House already did so, and Trump’s Republican allies in the Senate, uneasy over his move, are expected to follow suit. Many lawmakers view the declaration as an overreach of executive power. Congress appears to have enough votes to reject Trump’s action, but not enough to overturn his pledged veto.

The new border wall request is coming on top of the money Trump already has access to after declaring a national emergency last month. Trump took that step after Congress approved nearly $1.4 billion for border barriers, far less than the $5.7 billion he wanted.

Through the national emergency, Trump can tap an additional $3.6 billion from military accounts and shift it to building the wall. That’s causing discomfort on Capitol Hill, where even the president’s Republican allies are protective of their power to decide how to allocate federal dollars. Lawmakers are trying to guard money that’s already been approved for military projects in their states – for base housing or other improvements – from being shifted to build the wall.

The wall with Mexico punctuated Trump’s campaign for the White House, and it’s expected to again be featured in his 2020 re-election effort. He used to say Mexico would pay for it, but Mexico has refused to do so.