For all the strenuous efforts to keep California’s bullet train from leaving the station, the megaproject has acquired a certain locomotive-like momentum. With billions spent, more borrowed and bridges built, a high-speed rail line connecting San Francisco to Los Angeles looks more than ever like a question of when rather than if.

That is nevertheless a big question. With the California High-Speed Rail Authority in the midst of a shakeup and its detractors ascendant in Washington, the project faces obstacles that could keep it going nowhere fast for years. Even the official timeline doesn’t have the first phase completed for more than a decade, and it has already missed forecasts by an estimated seven years and $24 billion. Much of the disillusionment with the project can be traced to such unrealistic projections.

The rail agency itself is at a junction now that chief executive Jeff Morales has announced his resignation, the latest in a series of high-level departures. After five years running the nascent railroad, Morales told The Chronicle his leaving should not be read as an ill omen, saying, “We’ve made a tremendous amount of progress, from being at a standstill to having $3 billion-plus of construction under way.” In a valedictory letter to the rail authority board and the project’s most powerful friend, Gov. Jerry Brown, Morales took occasion to lash out at the bullet train’s “pusillanimous critics.”

Pusillanimous or not, those critics have often succeeded in slowing high-speed rail to a crawl. At the behest of Republicans in the state’s congressional delegation, who see the project as a boondoggle, Transportation Secretary Elaine Chao is pointlessly holding up $647 million in federal funding for Caltrain electrification, which would clear high-speed rail’s path up the Peninsula to San Francisco.

The bullet train project’s budget also relies on future federal funding that seems unlikely under President Trump, as well as private money that has yet to materialize. Even its state support through California’s cap-and-trade program took a hit when revenue from pollution permit auctions fell short of expectations.

The uncertainty about long-term funding, particularly of the line’s difficult and crucial crossing of the Tehachapi Mountains, has prevented construction beyond the small Kern County town of Wasco. That means the railroad isn’t quite connecting San Francisco to Bakersfield, let alone Los Angeles.

Still, Morales has a point about progress. Workers are building overpasses, realigning roads, and digging trenches at 11 Central Valley sites. More than eight years after voters narrowly approved nearly $10 billion for the rail line, the authority has issued its first bonds for construction. And last week, a Sacramento County judge ruled against the latest lawsuit, on behalf of Kings County and others, to block further bullet train spending on the grounds that it would be at odds with what voters approved.

Meanwhile, the state’s oversubscribed transportation infrastructure bears the growing burden of insufficient housing in San Francisco, Los Angeles, and their suburbs. Tens of thousands of Californians are commuting between the Bay Area and the emerging metropolises of the Central Valley by car. Just paying the state’s $52 billion road repair bill through higher taxes and fees took a herculean political effort in Sacramento this month, including an agreement to extend an East Bay-to-Stockton commuter rail to secure rural support. According to one analysis, even that huge amount of money won’t do the job. And air travel is only getting more crowded, cumbersome and, occasionally, violent.

It’s ironic that the greatest external threat to California’s high-speed rail may be a president ostensibly obsessed with Asia’s rise and America’s decline. Often held up as evidence of China’s prowess, high-speed rail is a fixture throughout the industrialized world. Like many monumental public works before it, the bullet train could be as admired on completion as it has been abhorred in creation.

The imperative, as for all trains, is getting there.