A ruling from the Senate parliamentarian gives Democrats more flexibility as they seek to pass other key items on President Joe Biden's agenda like his infrastructure plan and forthcoming bill on other domestic priorities and overcome GOP opposition to his administration. But challenges still lie ahead if Democrats ultimately decide to pursue the budget reconciliation process again.Democrats have already used budget reconciliation – the tool that lowers the threshold to advance legislation in the Senate from 60 to 51 votes in very limited circumstances relating to spending measures – to push through Biden's $1.9 trillion coronavirus relief package last month. With an extremely thin majority in the 50-50 split Senate, the vehicle allows Democrats to pass bills without any GOP support and avoid a filibuster as long as their party remains unified.Senate parliamentarian Elizabeth MacDonough ruled that the budget resolution from fiscal 2021 – which was used for COVID-19 relief – can be amended and used for another bill, according to a Monday evening statement from an aide to Senate Majority Leader Chuck Schumer of New York. In addition to the favorable ruling, Democrats will also have another opportunity to use the reconciliation process for the budget resolution in fiscal 2022.The parliamentarian, who is tasked with delivering rulings over Senate procedures, played a pivotal role during the reconciliation process to pass the relief bill, ruling that Democrats couldn't include a $15 minimum wage increase. Republicans have yet to weigh in on MacDonough's latest ruling, which hasn't been publicized. Plus, Democrats acknowledge that "some parameters still need to be worked out.""The parliamentarian has advised that a revised budget resolution may contain budget reconciliation instructions. This confirms the leader's interpretation of the Budget Act and allows Democrats additional tools to improve the lives of Americans if Republican obstruction continues," a Schumer spokesman said in a Monday evening statement.Still, Democrats haven't committed to definitively using budget reconciliation for the next big spending package as they assess whether bipartisan compromise is achievable – a sentiment reiterated by the White House on Tuesday.White House press secretary Jen Psaki told reporters that the administration is engaging with both parties and will invite back members next week to address infrastructure.But with Republicans signaling their opposition to the White House $2.25 trillion infrastructure plan and the tax increases proposed to pay for the bill, it's increasingly likely Democrats will need to revisit the budget process. Senate Minority Leader Mitch McConnell of Kentucky has vowed to "fight them every step of the way," diminishing any chances of at least 10 Republicans joining Democrats to advance legislation without using budget reconciliation.Democrats have floated two separate bills to enact major Biden priorities – one for physical infrastructure needs like roads, bridges, trains and ports and another for people-focused policies to address economic inequities like child care, paid leave and higher education. The ruling suggests that the party could use reconciliation at least two more times to pass both plans."While no decisions have been made on a legislative path forward, using Section 304 and some parameters still need to be worked out, the parliamentarian's opinion is an important step forward that this key pathway is available to Democrats if needed," Schumer's spokesman said.The Congressional Budget Act of 1974, Section 304, stipulates that after a resolution has been agreed to and before the end of the fiscal year on Sept. 30, "the two Houses may adopt a concurrent resolution on the budget which revises or reaffirms the concurrent resolution on the budget for such fiscal year most recently agreed to."But using reconciliation is not without its challenges, especially in a 50-50 Senate with a broad Democratic caucus. Because they need all 50 Democrats and Vice President Kamala Harris as the tie-breaking vote to pass bills through the process, they can't afford to lose any support.Democratic Sen. Joe Manchin of West Virginia said that he believes changes need to be made to the current version of the infrastructure plan to win his support. He's opposed to raising the corporate tax rate from 21% to 28% and believes it should be closer to 25%.And he suggested that around half a dozen other Democrats feel similarly, arguing they will have considerable influence in crafting the legislative text of the spending bill."I've had some outreach from the White House, but it was more heads up than input into the development of the package so I've already expressed some concerns," Democratic Sen. Mark Warner of Virginia told reporters at the Capitol on Monday, though he wouldn't comment on the details of that conversation or whether he supports a 28% corporate tax rate.Schumer could be tasked again with the tall order of keeping all of his members in line. During the passage of the COVID-19 relief bill, the Senate stalled for hours as Democrats negotiated behind the scenes for Manchin to vote with the party on their amendment related to enhanced federal unemployment benefits.Manchin ultimately backed the proposal, but it highlighted the challenges Democrats will face every time they try to shepherd legislation through budget reconciliation. And during a Monday interview, the West Virginia senator bluntly laid out the critical role he – and other moderate Democrats – play in whether or not Biden's agenda goes anywhere."The bill, basically, is not going to end up that way," Manchin told West Virginia Metro News in a radio interview. "If I don't vote to get on it, it's not going anywhere."