Americans have begun casting ballots in critical midterm elections across the United States, launching a marathon voting day that will determine the legislative balance of power in Washington.

The first in-person polling stations opened at 5:00am local time in Vermont, Al Jazeera reported, marking the commencement of an electoral cycle that will see tens of millions of citizens decide the composition of the US House of Representatives, the Senate, and dozens of state governorships.

Staggered voting across six time zones

Because the United States spans multiple geographic regions, voting proceeds in a gradual westward wave over nearly an entire day. Following Vermont’s early start, the majority of polling booths along the eastern seaboard—including pivotal battlegrounds such as Pennsylvania, North Carolina, and Georgia—opened between 6:00am and 7:00am local time.

Polling stations in central states, followed by mountain and Pacific regions, opened progressively thereafter. Polling will conclude latest in Alaska and the remote islands of Hawaii, where booths remain open until after midday on Wednesday, Australian Eastern Daylight Time (AEDT).

The staggered timetable means preliminary exit polling and early vote tallies will filter through to international observers while voters on the American west coast are still lining up to cast their ballots.

Control of Congress hangs in the balance

At stake in the nationwide ballot are all 435 seats in the US House of Representatives and 34 seats in the 100-member Senate. Historically, mid-mandate elections serve as a stern referendum on the sitting president, frequently resulting in governing parties losing control of one or both chambers of Congress.

Campaign analysts noted that unprecedented sums—equivalent to tens of billions of Australian dollars—have flowed into television advertising, digital campaigning, and ground mobilisation across an electorate sharply divided over inflation, healthcare, abortion rights, and foreign policy.

The outcome will decide whether the White House retains a legislative conduit to pass major domestic legislation and judicial appointments, or faces two years of intense legislative oversight, budget stand-offs, and committee inquiries spearheaded by a hostile opposition.

Strategic implications for Canberra

The contest is being tracked meticulously in Canberra, where foreign policy analysts and senior government officials are assessing the potential reverberations for the Australia-US alliance.

A divided Congress or an opposition-controlled House could inject fresh uncertainty into US defence spending appropriations, specifically elements crucial to the trilateral AUKUS pact. While support for Australia’s acquisition of nuclear-powered submarines has retained broad bipartisan backing on Capitol Hill, isolationist sentiment among vocal factions poses ongoing scrutiny for strategic investments and regional funding commitments in the Indo-Pacific.

Australian financial markets also opened cautiously, with currency traders monitoring the Australian dollar amid forecasts of volatility against the greenback as initial tallies are returned.

Complex count likely to delay definitive results

Election authorities across several key states have cautioned that definitive outcomes may not be known for days. The widespread use of postal voting, stringent verification procedures, and differing state laws governing when mail-in ballots can be processed mean that tight races could take significant time to resolve.

In several states, statutory recounting thresholds and potential judicial challenges may prolong the uncertainty, leaving the final composition of the incoming Congress in question well into the week.