NORTON, Mass. (WPRI) — Massachusetts voters are about to make decisions that could affect how the region is represented in Washington for years to come.

One of the biggest primaries ever in the Bay State will reach its grand finale on Tuesday, as voters pick a winner in the marquee Democratic contest for U.S. Senate between incumbent Ed Markey and challenger Joe Kennedy, as well as the crowded race to replace Kennedy in the U.S. House.

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While Markey has held only one event in Southeastern Massachusetts in recent days — a Friday rally in New Bedford — Kennedy has visited Bristol County twice and is set to return on Tuesday for a final swing.

Meanwhile, in the race to succeed Kennedy in the 4th Congressional District, only two candidates — former Brookline Select Board member Jesse Mermell and Newton City Councilor Becky Grossman — held publicly announced events in Bristol County on Monday.

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Mermell and Grossman are two of seven candidates seeking the Democratic nomination in the 4th District. A poll Sunday showed Mermell and Newton City Councilor Jake Auchincloss effectively tied.

Massachusetts Secretary of State William Galvin said Tuesday he expects high turnout in the primary, with roughly 850,000 ballots cast so far and the potential for as many as 1.2 million to 1.3 million in the Democratic primary alone when all is said and done.

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While polling places will be open from 7 a.m. to 8 p.m. Tuesday across Massachusetts, a majority of voters are expected to cast ballots by mail due to the pandemic. Mail ballots must arrive at local elections offices by 8 p.m. Tuesday in order to be counted.