The 3 economic pledges that will shape Biden's $4 trillion bareknuckle fight over infrastructure

• Biden is entering a more complicated phase of his presidency, as the fight over his infrastructure plans drags on.
• Biden's pledges will be tested, including no tax hikes for families earning less than $400,000.
• McConnell said on Wednesday that "100% of my focus is on standing up to this administration."

With the first 100 days behind him, Joe Biden is entering a new phase of his presidency - one with the capacity to be a lot messier than the initial three months of the administration.

The White House is now gearing up to shepherd $4 trillion in new spending plans through the cauldron of Congress. Democrats have paper-thin majorities in both the House and the Senate, where their control stems from Vice President Kamala Harris's tie-breaking vote.

Biden has brought up and doubled down on three economic pledges over the past week:

• No tax hikes for families earning below $400,000,
• Willingness to negotiate with Republicans on infrastructure package, and
• No deficit-spending on his long-term economic plans.

These promises are setting the parameters for the Biden administration's next stage and test the limits of the president's economic ambitions even within his own party, given the strong Republican opposition to his proposals.

Roadblocks ahead for federal spending and tax hikes

The White House is likelier to face more roadblocks compared to its push to quickly pass $1.9 trillion in emergency virus relief spending earlier in the year. Some of it in the two-pronged negotiation process will arise from Democrats themselves.

"As far as I can tell, this next tranche of spending will be a lot more difficult to get done than the last one," Jim Manley, a former aide to Senate majority leader Harry Reid (D-Nev.), told Insider. "Not only am I not convinced that Republicans are going to play ball, but there's also some differences with Democrats - not only in the House, but the Senate as well - about how to proceed."

Centrist Democrats are already pushing to trim some of the tax hikes that Biden has laid out, largely focused on fetching new revenue from multinational firms, high-earners and other wealthy Americans.

Sen. Joe Manchin (D-W.Va.) said he favors a 25% corporate tax rate, lower than the 28% level the president called for. He's also insisted on Democrats cooperating with Republicans on a wide range of issues, including the economy.

Manchin isn't alone on corporate taxes. Sen. Mark Warner (D-Va.) told NBC News on Tuesday that he "probably wouldn't go as far" as Biden on a corporate tax increase. He also voiced some disapproval with the White House's early move to rule out user-fees.

"I wish the president had not taken user fees off the table, whether it be a gas tax or whether it be vehicle-miles traveled," Warner said. "I think user fees make sense and they need some bipartisan support."

User-fees enjoy strong support from Republicans, who argue infrastructure spending should financed by people who benefit from the federal investments - essentially, the people who will drive on a repaired road or bridge should pay for it.

A group of Senate Republicans led by Sen. Shelley Moore Capito put forward a $568 billion infrastructure counteroffer mostly focused on roads, bridges, water systems, and broadband in mid-April. That part of the plan is unlikely to gain the administration's backing.

White House Press Secretary Jen Psaki said last month that user-fees would violate Biden's tax pledge, which she described as a "line in the sand for him."

On another front, Biden is still attempting to cut a deal with the GOP on infrastructure. Psaki recently said he's meeting with Capito and other Republicans at the White House next week. It remains unclear if they can strike an agreement given wide differences on the scope of their spending plans and who should pay for them.

Senate Minority Leader Mitch McConnell (R-Ky.) drew a red line of his own on Monday, saying Republicans would not go above $600 billion for an infrastructure plan, an amount less than a fifth of Biden's spending proposals. Two days later, he said at a press conference in Kentucky that "100% of my focus is on standing up to this administration."

Other Democratic bills on voting rights, immigration, and DC statehood have garnered no GOP support.

"As far as I can tell, Sen. Manchin is the only Democrat left on Capitol Hill that still thinks it's possible to cut deals with McConnell," Manley said.