Vice President Pence broke records and played a pivotal role as a tie-breaker in the Senate during 2017.

He could become even more essential to passing President Trump Donald John TrumpGOP divided over impeachment trial strategy Official testifies that Bolton had 'one-on-one meeting' with Trump over Ukraine aid Louisiana governor wins re-election MORE’s legislative agenda when the already-thin Republican majority narrows even further in 2018.

“The vice president does a lot of things that are invisible,” said Joel Goldstein, a law professor at St. Louis University who studies the vice presidency. “Breaking a tie vote is visible. It’s one of the most visible things the vice president does.”

In visible contributions, it was a record-breaking 2017 for Pence. He broke a tied Senate vote more times — six — than any other vice president during their first year in office.

Pence was also the first vice president to use his tie-breaking power to confirm a nominee to the Cabinet.

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Pence’s first tie-breaking vote was Feb. 7, just weeks after inauguration, in the vote to confirm Trump nominee Betsy DeVos Elizabeth (Betsy) Dee DeVosDeVos forgives 1,500 student loans amid federal lawsuit Warren campaign launches 'a calculator for the billionaires' after Gates criticism Education Department finalizes new regulations to relax college-accreditation requirements MORE as secretary of Education.

Since then, he has cast five more tie-breaking votes.

Pence’s office did not return a request for comment for this story.

Other vice presidents have averaged a little more than one tie-breaking vote per year. The last vice president, Joe Biden Joe BidenBudget official says he didn't know why military aid was delayed: report Growing 2020 field underscores Democratic divide READ: Foreign service officer Jennifer Williams' closed-door testimony from the House impeachment inquiry MORE, did not cast a single tie-breaking vote during his eight years in office.

John Calhoun, the vice president to President Andrew Jackson, cast the most tie-breaking votes of any other vice president, at 31, according to the Senate Historical Office.

Pence was able to make the difference for several Trump-backed agenda items, casting the deciding vote in favor of a tax-related amendment allowing money set aside in college savings plans to be used for other types of schooling; blocking new regulations allowing consumers to sue their banks; starting debate to roll back parts of Obamacare; overturning a rule that blocked states from withholding funding for Planned Parenthood; staring debate on that same rule and confirming DeVos.

Not everyone sees Pence's role as significant.

“Just about anybody can cast a deciding vote, I think vice presidents are more significant than that,” said Ted Kaufman (D), a former Delaware senator and chief of staff to Biden during his time in the Senate.

Goldstein pointed out that Pence’s ability to break a tie results from a unique combination of factors in the current Senate.

Former Senate Majority Leader Harry Reid Harry Mason ReidThe Memo: Democrats confront prospect of long primary Bottom Line Lobbying world MORE (D-Nev.) in 2013 weakened the power of the filibuster, which was often used by the minority party to delay confirmation votes. He pushed through rules that reduced the number of votes required for Senate approval of executive and judicial nominees from 60 votes to 51 votes.

Republicans have also passed legislation this year under reconciliation rules that only require 51 votes. In a vote that requires more than a simple majority, no tie-breaker would be required.

Plus, a number of legislative items the Republicans tried to push through in 2017 only appealed to one party, so the GOP needed every vote to pass legislation without any Democratic support.

The vice president is technically the president of the Senate, which is largely a symbolic position until a tie occurs. Then, Senate rules allow for the vice president to cast a vote. That power has been mighty in Trump’s young administration, while Republicans held a narrow 52-48 majority in the Senate.

“The combination of the changes in the filibuster rule, plus the fact that it was 52-48, and the fact that they were proceeding on a partisan basis so the available pool was really only 52 votes versus 100 votes was really all together what made the difference,” Goldstein said.

The Republican majority in the Senate will narrow even further to 51-49 on Jan. 3, when Pence will swear in Democrat Doug Jones as the freshman senator from Alabama.

But Pence’s importance as a tie-breaker in 2018 will depend on whether Republicans reach across the aisle, whether they can lock in support within their own party and the type of votes brought to the floor.

For example, there will likely be fewer controversial nominees in the second year of Trump’s administration, compared to the first.

Still, Trump and the Republican Congress have an ambitious legislative slate heading into the new year, including infrastructure funding; a fix for the Deferred Action for Childhood Arrivals program, which allows certain young immigrants to live and work in the United States; and possibly another run at cutting away at ObamaCare.

If Pence becomes even more indispensable in the Senate, it could affect his other responsibilities.

The vice president already had to delay a trip to Israel in December in order to preside over a vote on the GOP tax bill. Ultimately, Pence was not needed to break a tie on that legislation, which passed in a 51-48 vote.

“It’s a significant thing about the vice presidency and it brings attention to Pence, but it’s not as if he’s really exercising any discretion or independent judgement,” said Goldstein. “He’s basically doing what the administration’s line is to break the tie in its advantage. … It’s as if the Constitution now gives the administration a win whenever the Senate has a tied vote.”