Nearly 20,000 Bay State Democrats have fled the party this winter, with thousands doing so to join the Republican ranks, according to the state’s top elections official.

Secretary of State William Galvin said more than 16,300 Democrats have shed their party affiliation and become independent voters since Jan. 1, while nearly 3,500 more shifted to the MassGOP ahead of tomorrow’s “Super Tuesday” presidential primary.

Galvin called both “significant” changes that dwarf similar shifts ahead of other primary votes, including in 2000, when some Democrats flocked from the party in order to cast a vote for Sen. John McCain in the GOP primary.

The primary reason? Galvin said his “guess” is simple: “The Trump phenomenon,” a reference to GOP frontrunner Donald Trump, who polls show enjoying a massive lead over rivals Marco Rubio, Ted Cruz and others among Massachusetts Republican voters.

“The tenor of the Republican campaign has been completely different from what we’ve seen in prior Republican presidential campaigns,” Galvin said. “You have to look no farther than the viewership for some of the televised debates.

“The New York Times referred to the campaign as crude; I suppose that’s fair,” added Galvin, a Democrat. “The fact of the matter is the tenor has been very different this time. And that has an effect. People are interested. It’s exciting.”

Galvin said the state could see as many as 700,000 voting in tomorrow’s Republican primary, a significant number given just 468,000 people are actually registered Republicans. In Massachusetts. unenrolled — otherwise known as independent — voters can cast a ballot in the primary of any party.

If the Democratic vote is close to that of 2008 — when 1.2 million hit the polls — the state could surpass the 1.8 million that voted that year overall, setting what Galvin said he believes would be a record for a presidential primary in Massachusetts.

“The question in my mind is the Democratic turnout,” Galvin said. “The nature of the race is a little different than it was in ’08. … It’s a fact that Sen. (Bernie) Sanders has a very aggressive campaign here in Massachusetts. He spent both time and money. He has a good ground (game) from what I can see, as does Sen. (Hillary) Clinton. So that’s going to help us. But the chemistry was somewhat different than it was in ‘08.”

Galvin noted the historical context in 2008, when then-Sen. Barack Obama was vying to become the nation’s first black president, and running against Clinton — seeking, as she is again this year, to become the first woman to serve as president.

Turnouts have hit record levels in other primary states this year.

Galvin pointed to the shift in voters from the Democratic party as an “indicator” of turnout in the Bay State.

But while significant, it doesn’t necessary signal a change in the political power structure in Massachusetts, where Democrats have long dominated with heavy majorities in the legislature and across constitutional offices.

The 19,800 who left the Mass Dems represent about 1.3 percent of the 1.49 million enrolled in the party. And though the MassGOP gained several thousand voters, it actually lost more in the same time frame, when 5,911 quit the party to be unenrolled.