The US Senate has taken 36 votes so far in 2018. They passed a budget, failed on Dreamers (so far), and confirmed many Trump nominees. The chart below shows the groups of senators who vote most often with their colleagues. Various groups on both sides of the aisle emerge. These are senators whose votes correlate more than 90% of the time.
The main Republican block includes Thom Tillis (NC), Orrin Hatch (UT), Rob Portman (OH), Roger Wicker (MS), Todd Young (IN), Richard Shelby (AL), Thad Cochran (MS), Pat Roberts (KS), Shelly Moore Capito (WV), Roy Blunt (MO), Deb Fischer (NE), John Hoeven (ND), John Boozman (AR), and John Cornyn (TX). This group is largely made up of long serving senators and senators either in the GOP leadership or close to it. Mitch McConnell’s votes don’t highly correlate with this group but their votes represent the consensus position of the Republican leadership.
Another large group of Republicans include Jim Lankford (OK), Ron Johnson (WI), Chuck Grassley (IA), Jim Risch (ID), Mike Crapo (ID), and Richard Burr (NC). Their votes are distinct from leadership. Other small groups include Tom Cotton (AR) and David Perdue (GA) of legal immigration cuts fame, Mike Enzi (WY) and Ben Sasse (NE), and Jim Inhofe (OK), John Barrasso (WY), and John Thune (MT). Barrasso and Thune are in leadership but vote less often with the leadership consensus than others.
On the Democratic side, there are two large groups closely together. One contains Maggie Hassan (NH), Bob Casey (PA), Sheldon Whitehouse (RI), Bill Nelson (FL), Jeanne Shaheen (NH), Jack Reed (RI), Tammy Duckworth (IL), Gary Peters (MI), Debbie Stabenow (MI), Tim Kaine (VA), and Chuck Schumer (NY). The other group contains Ben Cardin (MD), Sherrod Brown (OH), Brian Schatz (HI), Martin Heinrich (NM), Tom Udall (NM), Tina Smith (MN), Chris Van Hollen (MD), Dick Durbin (IL), and Tammy Baldwin (WI). These groups are linked through Ben Cardin and Tim Kaine and Chuck Schumer. These senators are closest to the Democratic leadership.
A group liberal Democratic senators vote often with each and less with the leadership. This includes Ed Markey (MA), Bernie Sanders (VT), Kirsten Gillibrand (NY), Jeff Merkley (OR), Kamala Harris (CA), Elizabeth Warren (MA), and Cory Booker (NJ). Other distinct groups include Mark Warner (VA) and Amy Klobuchar (MN), Maria Cantwell (WA) and Michael Bennet (CO), Angus King (I-ME) and Tom Carper (DE), and Robert Menendez (NJ), Chris Murphy (CT), Jon Tester (MT), and Pat Leahy (VT).
The other half of the Senate have more individualistic voting patterns.
Zooming out, looking at basic correlation (50% or higher), unsurprisingly shows the two distinct parties.
Joe Manchin (WV) and Joe Donnelly (IN) serve as the bridge between the two parties. Manchin correlates with Donnelly and Republican Shelly Moore Capito (WV). Donnelly correlates with Heidi Heitkamp (ND) who then correlates with the blob of Democratic senators. The Republicans have more outliers from the party core. Ron Paul (KY), Mike Lee (UT), Jeff Flake (AZ), Johnny Isakson (GA), Lamar Alexander (TN), Mike Rounds (MT), Ted Cruz (TX), Susan Collins (ME), Cory Gardner (CO), and Lisa Murkowski (AK) break most often from the party and from each other. The Democrats are voting more cohesively this year.