(Bloomberg) -- The personality-driven, mudslinging presidential campaign notwithstanding, Americans aren't just choosing between two people on Election Day. More than 130 million voters are expected to determine whether the next occupant of the Oval Office starts off with a mandate—and the allies in Congress to implement it—or with enemies and further gridlock, with the Supreme Court, the economy, Obamacare, and even the health of the planet possibly hanging in the balance.
There’s an 83 percent probability of a divided government
Although these sensitive calculations will shift around before Tuesday, Hillary Clinton is still the odds-on favorite to win the presidency, Democrats are slightly more likely to win back the Senate, and Republicans are expected to retain comfortable control of the House of Representatives. There's been a three-percentage-point increase in the odds of a divided government since Friday, according to prediction market aggregator PredictWise, one of the most accurate and comprehensive forecasters in our primary prediction analysis.
But that's just one scenario. Here's a look at the range of possibilities, and the chances they will happen.
There’s a 61 percent probability of a President Clinton, a Democratic Senate and a Republican House
This is the likeliest combination, according to PredictWise, down four points from Friday.
This outcome would give Clinton some leverage in the looming battle over replacing Justice Antonin Scalia on the Supreme Court, which has often split four justices to four since the February death of the conservative icon, and could stop Clinton from having to veto any bills dismantling President Obama's healthcare law. It would also likely mean deadlocks on other laws and spending, with House Republicans acting as the "check" on the White House.
But Clinton's presidential odds have slipped in recent weeks—from as high as 93 percent in the New York Times' poll-driven Upshot model—amid previously reluctant Republicans coming around to Trump and the FBI announcing it wanted to examine new evidence in the investigation of Clinton's private e-mail server. Other poll aggregators, including RealClearPolitics, Huffington Post, and Bloomberg Politics' own Poll Decoder have showed similar trends.
Among the reasons she's still a favorite: her strength in states rich in electoral votes, her enduring poll lead, and an edge in early voting.
An analysis by polling and strategy firm Clarity Campaign Labs shows Clinton winning 52.5 percent of votes cast nationwide through Nov. 6 and leading in several key battleground states, including Wisconsin, North Carolina, and Colorado. The company models the likelihood that an early voter will pick either Clinton or Trump using an algorithm that weighs hundreds of variables—from individual voting histories to neighborhood-level Census records—in order to determine how much they resemble each candidate's typical supporter. Translated into electoral votes, this early voting model puts Clinton at 244 to 149 for Trump, not counting votes from any of the 13 states requiring an excuse to vote early or absentee. If Clinton wins just one of these, reliably blue New York, she'll surpass the 270 electoral votes needed to win.
When it comes to the Senate, Democrats have a 51 percent chance of flipping at least five seats to control a clear majority, according to PredictWise; there's an additional 23 percent chance of tying with the Republicans, in which case a Vice President Tim Kaine would cast the deciding vote. The states where Democratic gains are most likely (in descending order) are Illinois, Wisconsin, Pennsylvania, New Hampshire, and Indiana.
Republicans, meanwhile, have a 94 percent chance of holding on to the House.
There’s a 22 percent probability of a President Clinton with a Republican Congress
This scenario will likely trigger some déjà vu for Clinton, whose husband spent six years as president facing off against a Republican-controlled Congress. Think politicking, gridlock, shutdowns, and investigations.
However, she's not likely to see as large of a bicameral Republican congressional majority as President Obama currently faces. While FiveThirtyEight currently favors Republicans in the race for the Senate, they have just a 0.4 percent chance of getting at least the 54 seats they presently hold, according to PredictWise. Their colleagues in the House, meanwhile, have similarly slim hopes of holding on to their historically large majority, but more than 90 percent odds of keeping numerical control of the lower house of Congress.
Likely soft spots for the Republicans include five congressional districts across Florida, Nevada, New Hampshire, and Virginia denoted "Likely Democratic" or "Lean Democratic" by the Cook Political Report, as well as five "Republican Toss Up" seats in districts that generally lean Democratic. The party would need to sweep most of the remaining 11 "Republican Toss Up" seats to hand Nancy Pelosi the Speaker's gavel.
There’s an 11 percent probability of a President Trump and a Republican Congress
There's a one-in-nine chance that Nov. 8 is a clean sweep for Republicans, a scenario that is three points less likely than Friday. In this outcome, a wave of voters would give GOP candidates a boost on the way to putting Trump at the top of a unified government, with a mandate that would include: rolling back regulations, enacting tax cuts, putting a staunch conservative (or two or three) on the Supreme Court, renegotiating trade deals, beginning the task of repealing and replacing Obamacare, and at least exploring the idea of building a wall on the U.S. border with Mexico.
While FiveThirtyEight.com gives Donald Trump a roughly 31-percent chance of winning the presidency, other projections put his odds much lower, including The Upshot (16 percent), reflecting varying inputs and weights in their respective models. Any late-breaking surge that pushes Trump to a surprise win will almost certainly carry down-ballot candidates—and control of the Senate—along with him.
Before the FBI news on October 28 regarding the investigation into Clinton's former e-mail server, the campaign described a narrow electoral path that required winning Florida and a grab bag of other swing states that were leaning toward Clinton, such as North Carolina and Nevada. As of last Thursday, it was talking about moving into traditionally Democratic states such as Michigan and New Mexico, as part of a $25 million ad buy by the campaign for the final week—though the latest ad reservation data from Kantar Media/CMAG analyzed by Bloomberg Politics shows no money allotted for either state yet.
Recent polling has suggested Trump may be able to grab some of those states, such as Nevada and North Carolina, where he's turned a RealClearPolitics deficit into a 1.5-point and 1.4-point lead, respectively. Meanwhile, targets such as Wisconsin and Pennsylvania are proving more stubborn, with Clinton holding on to healthy leads.
The currency markets, meanwhile, seem to see a shrinking opening for Trump: The Mexican peso, which has declined as Trump's chances are perceived to increase, is still weaker than when Trump officially won the nomination but has been strengthening in recent days.
There’s a 6 percent probability of a President Clinton with a Democratic Congress
A Democratic hat-trick looked increasingly possible in the weeks following Clinton's strong debate performances and the release of an Access Hollywood tape in which Trump claimed he gropes women, but it has fallen away as a possibility, now getting less than one chance in 16.
There is zero probability of a President Trump with a Democratic Senate and a Republican House
Because of the likelihood that Democratic gains in the Senate would also give the states to Clinton, the likelihood of Trump winning and then facing a divided Congress are negligible. Other scenarios are currently forecasted as being similarly improbable.