Increasingly since about 1972, voters have cast ballots for president and the Senate for members of the same party. If this pattern holds and Clinton wins, Democrats are likely to regain the majority in the Senate. Analysts rank the Senate races in eight or nine states as very competitive. In three of these — Wisconsin, Illinois and Indiana — the Democrat has a clear lead and seems poised to take a Republican seat away. At least five other races are frequently cited as toss-ups. Only one of these seats is held by a Democrat, Nevada, where Minority Leader Harry Reid (D-Nev.) is retiring.
So, if Clinton wins, the Democratic advantage will be formidable. However, in the event GOP nominee Donald Trump were to win, the Republicans might well hold their Senate majority narrowly.
But there is another possible outcome. The current Republican Senate majority is 54-46. A five seat pick-up would provide a narrow 51-49 Democratic majority.
What if the Democrats win four seats back, leaving the count in the Senate at 50-50? What then?
Article I, Section 3 of the Constitution states: "The Vice President of the United States shall be President of the Senate, but shall have no vote, unless they be equally divided." When the Senate ties, the vice president casts the deciding vote.
Therefore, if Clinton is elected, the vote cast by her running mate, Tim Kaine, on any tie will assure the Democratic Senate majority. If Trump were to win — with the technical complication that Joe Biden would still be vice president when the 115th Congress convenes on Jan. 3rd until the presidential inauguration on Jan. 20 — the Senate majority would be established by Mike Pence's vote.
A tied Senate may seem unlikely. After all, it has occurred only twice in all of American history. But some analysts rate a 50-50 Senate as the most likely outcome this year. For example, the current forecast by "The Upshot" at The New York Times indicates a 20 percent chance, one in five, more likely than any other outcome.
Even if the Senate is equally divided, the new president will be anxious to begin enacting her/his agenda. And, with a Supreme Court nomination likely pending early in the session (unless the lame-duck 114th Congress after the election were to confirm Supreme Court nominee Merrick Garland,) a great deal will be at stake quickly.
Beyond that, things are not so clear.
The 2000 election resulted in a tied Senate at the outset of the 107th Congress. The only other time this had ever occurred was in 1881 in a Senate so different that no precedents were useful. In January 2001, with newly elected Vice President Dick Cheney casting the deciding vote, the Republicans became the apparent majority.
But wait a minute.
The Senate requires one or more organizing resolutions to establish such things as the size of committees and their party ratios, committee chairmen and the appointment of senators to the committees. Other significant matters include such things as the allocation of committee space and funding between the parties is also addressed.
Here's where, in the bitterly polarized Senate, things could get sticky. The evenly divided Senate in January 2001 established some new precedents.
Then-Senate Minority Leader Tom Daschle (D-S.D.) described the circumstance at the outset of the 107th Congress. In his memoir, "Like No Other Time," he wrote: “The fifty-fifty split created an intriguing institutional challenge — determining who would control the chamber and set its agenda in this evenly divided Senate."
Daschle's Democrats immediately demanded to share the power with the Republicans.
"We wanted the budgets for each committee ... to be divided evenly between both parties. ... If the money and memberships were evenly divided, the chairmanships would be hardly more than cosmetic."
Reid, then the whip for the Democrats, boiled it down: "It's fairly simple. It takes a resolution to form committees in the Congress. And, of course, it goes without saying that that is something that doesn't happen with 51 votes. You have to have 60 votes."
The organizing resolution is a debatable matter in the Senate. That means if the minority senators feel they have not been fairly treated, they might filibuster. This possibility of filibuster has kept much of the organization of the Senate relatively routine. For example, reliably, committee ratios reflect the ratio of the full Senate. In the House, by contrast, the majority keeps a more than 2-1 majority in the all-important Rules Committee, no matter what the ratio in the House itself.
In the 107th Congress, the Senate Republicans made an agreement to share power with the Democrats. Committees were equally divided and other provisions weakened the normal powers of the majority leader.
With so much at stake, would the minority party in January, whether it's the Republicans or the Democrats, settle for anything less?