Michelle Wu has big ideas. If she’s elected mayor, Beacon Hill could decide if many of them happen.

Much of City Councilor Michelle Wu's platform, including seeking free fares on the T, would require action from the Legislature.JOSH REYNOLDS/Associated Press

Michelle Wu has built her campaign to be Boston’s next mayor on bold ideas, from eliminating fares on the MBTA to abolishing the city’s powerful development agency. Actually realizing them, however, will depend on a place where mayors have little control: Beacon Hill.

Boston’s voters are often courted with campaign promises that, whether quietly acknowledged on the campaign trail or not, hinge heavily on action or funding from the State House. But it’s a particularly acute reality this year for Wu, who’s vaulted to front-runner status in her head-to-head race with Annissa Essaibi George while wielding an ambitious platform.

Some of her most sweeping campaign ideas have faced and will face significant headwinds, even in a Democrat-dominated Legislature. And while the Boston mayor’s office offers an unrivaled bully pulpit in the city to push change, providing the funding for a quasi-state transit system to be free, for example, or raising certain taxes to pay for others are decisions that sit with state government, where the gatekeepers are a 200-person Legislature and a governor beholden to the entire state.

Wu has “very ambitious goals: ‘Let’s go after rent control. Let’s make the T free.’ . . . She’s at least put a marker out there to turn the system upside down. But this is not a system that is easy to move,” said state Representative Russell E. Holmes, a Mattapan Democrat who’s weighing whom to endorse in the race.

“I’m going to spend an enormous amount of time with my questions of attainable,” he said. “You can have a bold marker, but when do you anticipate achieving that?”

Beacon Hill has control over a variety of municipal-facing affairs, from building codes and allotting liquor licenses to whether a city can raise new forms of certain revenue. And many times, Boston needs the Legislature to approve a so-called home rule petition to put major changes into law.

Essaibi George has particularly seized on the viability of several of Wu’s plans, criticizing her fellow city councilor for pursuing unrealistic goals, notably in pushing for fare-free public transit that she calls “legislating by hashtag.”

Wu’s campaign, in turn, has repeatedly underlined that she has “the most support from Beacon Hill.” She has endorsements from at least 22 lawmakers, including from outside Boston, to Essaibi George’s one, offering evidence of her ability to forge relationships there.

“There’s consensus across the board that we have to be creative and bold to figure out how we quickly support our communities,” Wu said. “This is a time for collaboration and partnership.”

It’s not always easy. Former mayor Martin J. Walsh had been a state lawmaker and enjoyed a good relationship with Governor Charlie Baker, a Republican. Yet, he struggled to realize some priorities, either because they were rejected or lacked the necessary state funding. When he first ran in 2013, for example, Walsh promised free prekindergarten for all — something both Wu and Essaibi George are also pitching. But when he left office this year, the city was providing enough seats for just over half of Boston’s 4-year-olds, leaving Walsh to lament that the city needed “a larger commitment on a statewide level.”

Walsh scored a win on housing when lawmakers agreed this year to give the city more authority to extract affordable housing commitments from developers. But an earlier bid to help prevent tenants from being displaced — a key plank of Walsh’s housing platform midway through his tenure — fizzled in the Legislature.

Several parts of Wu’s platform lean on state buy-in. The Roslindale Democrat has called to eliminate fares on the MBTA, backed the restoration of rent control decades after Massachusetts voters banned it, and offered a plan to reshape development in the city, including by dissolving the Boston Planning & Development Agency.

They’re all actions that would require approval at the State House. She’s also proposed a “Boston Green New Deal,” a sweeping environmental plan that includes, among other provisions, speeding up deadlines to reach citywide carbon neutrality and installing more solar infrastructure on municipal buildings — actions within the city’s authority. But the plan also advocates for free public buses and raising the gas tax to pay for it, which would specifically require legislative action.

Baker, for one, has rejected the idea of restoring rent control, and such proposals in the Legislature have so far faltered. Democratic leaders in the Senate and House have repeatedly wrangled with calls to infuse the MBTA with more funding, but they have never publicly broached plans about replacing the hundreds of millions of dollars the quasi-public agency collects each year in fares should they be eliminated.

Asked about the fare-free push, Aaron Michlewitz, a Wu supporter and North End Democrat who leads the powerful House budget committee, said policymakers shouldn’t rule out any idea for improving the T, but the “primary focus” should be stabilizing the agency’s finances and providing better service.

“I feel confident that we’ll be able to accomplish a lot of things together. But we will have to have some frank and difficult conversations,” Michlewitz said of Wu, should she be elected. “That’s what’s supposed to happen.”

Wu supporters say there is appetite for reshaping the city’s planning and development process. But whether the Legislature would agree to effectively abolish the agency, as Wu has called for, is unclear. Its former iteration was established under state law, meaning the lawmakers would have to approve such a change.

“I was with Bernie Sanders [in the presidential election], and Michelle does this too: They throw out these very almost impossible ideas. But the reality is, if you’re not thinking big, then you’re not really thinking,” said state Representative Michael J. Moran, a Wu supporter and the House’s assistant majority leader.

“I don’t think for a minute she’s going to abolish the [BPDA],” the Brighton Democrat said. “But is she going to make some big changes, like going to separate permitting and planning? We do need to streamline it.”

To be sure, the mayor wields wide authority over the city’s sprawling bureaucracy and has the ability to realize plans unilaterally or with the City Council’s blessing. Wu, for example, has said she would emphasize a public health-centered focus on policing, such as hiring more counselors — decisions that are far beyond Beacon Hill’s consideration.

“When we talk about big issues like climate justice, of course that involves global and statewide implications,” Wu said. “But it’s also how we double our street-tree canopy to clean the air. It’s converting to electric school buses. All of these issues at the city level start from the day-to-day impacts on people’s lives. There’s always a way to make progress.”

Essaibi George’s own platform appears to rely less on needing state approval for various ideas than building on existing ones. Still, some details of her agenda also could collide with Beacon Hill’s more deliberate pace.

While both candidates have pushed universal pre-K, Essaibi George has promised to offer it in her first 100 days, which would likely require an influx of substantial funding, including state help. Walsh’s administration estimated early in his first term that it would cost $56 million to make quality, full-day preschool available to all the city’s 4-year-olds.

“We can support efforts that are already happening at the State House,” Essaibi George said. “It doesn’t have to initiate at the city [level].”

Both candidates, at least for a year, would also have to work with Baker, whose office, for example, is currently involved in helping identify ways to ease the humanitarian crisis at the intersection of Massachusetts Avenue and Melnea Cass Boulevard. Baker has not said whether he’ll seek a third term next year.

Essaibi George said she’s confident she can work with “whoever it is” in the governor’s office. Wu said she wants to ensure the city’s needs “are heard loud and clear.”

But would that be easier with a Democrat?

Wu answered in one word. “Yes.”