President Joe Biden faces a 50-50 Senate and a narrowly divided House. Some observers assert that with House Speaker Nancy Pelosi holding the gavel and Vice President Kamala Harris able to preside as president of the Senate and vote to break ties, the Democrats control Congress.

Looking at mathematic “control” of Congress betrays a simplistic understanding of the very human endeavor of representative government, boiling the system down to mere numbers as if it were a business with a balance sheet.

Politics, more so than business, is about people, not numbers. In business, if you don’t make a profit for too long, you’ll go bankrupt and people will lose their jobs. It’s almost the opposite in politics—at least among lawmakers as opposed to chief executives like the president and governors—in that getting elected and reelected is largely disconnected from the effects of policies lawmakers voted for. In politics, success and failure attach personally and have little to do with job effectiveness.

What does count is relationships. Psychology. Communications. Perception. People love winners and optimists. People want to be respected and loved. Lawmakers are no exception. Frequently, the human aspect of governing affects the numbers.

We’ve Had a Close Senate for a Long Time

Since 1980, when the Republicans took the U.S. Senate for the first time in 26 years with the election of Ronald Reagan, the Senate has had a partisan margin of 51 or 50 for eight out of 40 years.

On May 22, 2001, the new George W. Bush administration was only four months old when 80-year-old Jim Jeffords, a liberal Republican senator from Vermont, announced he was likely crossing the aisle. Two days later, he did and the 50-50 margin (with Vice President Dick Cheney breaking the tie) was shifted to 51-49, putting Tom Daschle, D-S.D., in charge as majority leader. Later in that same session of Congress, Sen. Paul D. Wellstone, D-Minn., died on Oct. 25, 2002, with Independent Dean Barkley appointed to fill the vacancy.

Jeffords had long been drifting away from the GOP. A Yale University undergrad, a Harvard Law School graduate, and son of a state chief justice, Jeffords served 30 years in elected office by the time he won a U.S. Senate seat in 1988. He had the lowest lifetime American Conservative Union rating of any Republican senator, due to him favoring abortion, opposing tax cuts, and being one of only two Republican senators to oppose Clarence Thomas’s nomination to the U.S. Supreme Court.

Jeffords might have been content at this late stage of his career to soldier on as an old-school New England Republican. But the new Bush administration, pre-9/11, had an ambitious social agenda and wanted tax cuts to lift the nation out of the recession that followed the dotcom bust.

The former was problematic for Jeffords, especially as the proposals came from a Texas conservative. Further, due to the 50-50 tie, Vice President Cheney started to spend more time in the Senate, with some referring to him as the “101st senator.” By April 3, 2001, Cheney cast his first tie-breaking vote in the Senate and then cast another one two days later.

Within seven weeks, Jeffords switched parties and Cheney’s role as a tiebreaker would only be used one more time while the Democrats held the majority during the 107th Session of Congress.

Joe Biden Was There

This recent history is likely still clear in the minds of many senators—and certainly the mind of Biden, who in 2001 was serving his 28th year in the U.S. Senate. This likely means Harris will be kept far from the U.S. Senate, where she only served a year before it was expected she would run for president, which she made official in January 2019. The credible fear is likely that Harris becoming a “101st senator” could push a more moderate Democrat like West Virginia’s Joe Manchin into the arms of neighboring Kentucky Republican Mitch McConnell.

In addition to relationships and pride, mortality can play a role in Senate history. Eight years after Jeffords’s switch, the Senate saw a different kind of power shift when, in 2009, Sen. Ted Kennedy died at the age of 79. His seat was temporarily filled by former Sen. Paul Kirk, a Democrat, until a special election on Jan. 19, 2010.

In an election that presaged the Tea Party year, Scott Brown won the Massachusetts seat. Brown’s election deprived Senate Democrats of 60 votes to invoke cloture, a procedural vote limiting debate—in other words, ending the possibility of a filibuster to bring a vote to the floor of the Senate.

This unexpected loss of the Democrats’ 60-vote majority changed the strategy to pass the Affordable Care Act, moving it to a budget reconciliation process that enabled Senate passage with only 51 votes. This later had significant consequences as it opened constitutional vulnerabilities to the law.

Congresses Often See Some Movement

It’s not uncommon for legislative bodies to lose members during session. In my six years in the California legislature, with 120 members, we lost two to death by illness. It made little political difference in a body with overwhelming partisan majorities.

Compared to Congress, state legislatures tend to have younger members. Since 2000, 32 of the 535 elected officials who comprise the U.S. House and Senate have died in office. And, unlike in California, the passing of a member in either house could have significant political ramifications.

So, what is the likelihood of the Senate continuing 50-50 to the end of the 117th Congress? Slim. Democratic Sen. Patrick Leahy, 80, of Vermont was hospitalized for a few hours on Jan. 26 “out of an abundance of caution” after not feeling well.

Looking only at the annual probability of death by sex and age per the Social Security Administration, only considering members 60 and older, and only taking into consideration senators in states represented by a governor of the opposing party, there is a 35 percent probability that a Republican senator will die and be replaced by a Democrat in the next two years. Conversely, there is a 65 percent chance of the same happening to the Democrats. Also, some states allow for an appointment to serve until the next regularly scheduled federal election, while others require a special election as happened in Massachusetts in 2010.

The point is that the current arrangement in the Senate is very fragile. This might be a contributing factor to why both Sens. Manchin and Kyrsten Sinema, D-Ariz., indicated they won’t agree to ending the filibuster. They know all too well that the odds are high that the Senate won’t remain tied through the next election in 2022.

Congress Is Too Tight to Take Risks

Our national legislative arrangement is bicameral, as it is in all the states except Nebraska. Since the filibuster will continue in the Senate, this has a significant effect on the U.S. House, which is more narrowly divided than it’s been in 20 years.

House members, especially Democrats in competitive districts, will likely be reluctant to vote for a controversial bill only to see it die in the Senate without a vote. There are enough of them to prevent a bill from passing. Lawmakers are excellent at avoiding all-pain, no-gain situations.

Add to that the huge difference in leadership energy, style, and recent success between Pelosi and House Minority Leader Kevin McCarthy. Pelosi, 80, just came off a bruising campaign season where, instead of increasing her margin in the House as widely expected, lost nine seats. She holds sway by experience and fear.

In contrast, McCarthy, who was also the Republican leader in the term-limited California State Assembly, is 56, charismatic, and has the benefit of having just guided his caucus to picking up seats against all odds. Most observers expect McCarthy will be speaker after the midterm elections.

This leadership dynamic will affect votes. People like a happy winner and will more willingly follow them. McCarthy is far more likely to hold his caucus together for tough votes than is Pelosi hers.

The end result is that this Congress is likely to pass fewer bills of consequence than in the past 20 years, leaving the Biden administration to resort to rule by “pen” and “phone”—continuing the recent trend of expanding the power of the executive and of the administrative state.