President Trump has proposed a $54 billion increase in defense spending for 2018, but deep divisions on Capitol Hill are making any significant hike uncertain, according to Katherine Blakeley, a research fellow at the Center for Strategic and Budgetary Assessments.

First, a new Pentagon budget is likely to be delayed for months as Congress appears poised to pass another stop-gap budget called a continuing resolution at the start of the new fiscal year in October, Blakeley wrote in an analysis released Monday.

"Congress' window for funding defense — and the rest of the government — before the end of the 2017 fiscal year is short and closing fast," she wrote.

Lawmakers then face the daunting task of cobbling together a defense budget with varying opinions among Republicans about how big an increase is warranted, looming caps under the Budget Control Act, and Democrat opposition to non-defense spending cuts.

"The wide gulfs between the political parties and between the defense hawks and the fiscal hawks will not be closed soon," Blakeley wrote.

Trump released his $603 billion defense budget request in May, touting it as a major increase. It would bust through the $549 billion cap set by the BCA, a law passed by Congress in 2011.

Most of Trump's increase would go to shoring up existing forces after years of successive continuing resolutions, capped budgets and overseas deployments. The historic military buildup of ships, troops and aircraft that the president campaigned on will wait until 2019, according to the Pentagon.

Republican hawks in both the House and Senate, including Armed Services chairmen Sen. John McCain, R-Ariz., and Rep. Mac Thornberry, R-Texas, have called Trump's increase too small.

They generally agree that defense spending should go up by about $30 billion. But in recent weeks committees in both chambers have passed defense authorization and spending bills with differing amounts and different proposals for budgeting the hikes.

However, for any of the increases to happen, Congress must first come together to raise the $549 billion spending limit set by the BCA.

"The most pressing question of the debate about the FY 2018 defense budget is whether Congress will be able to raise or remove the statutory caps that limit national defense spending," according to Blakeley.

Lawmakers have amended the caps three times in the past but never agreed to such large hikes. Past budget agreements allowed an extra $9 billion to $27 billion, Blakeley said.

Trump has complicated the effort to reach a deal on raising the caps by calling for all of his proposed $54 billion increase to be offset by cuts to non-defense programs. The move has incensed Democrats who could stand in the way of his budget and any deal in Senate.

"As it did in the three previous deals to amend the BCA caps, Congress could reach a bipartisan deal," Blakeley wrote. "However, any regular bill to raise the BCA caps would require the votes of eight Democratic senators to vote for cloture."

The hurdles "make it difficult to see how a substantial defense buildup … can be realized," she wrote.