The 114th Congress is now in session and the environment is decidedly Republican. The GOP took control of both chambers of Congress after the midterm elections, in which only 36 percent of voters participated. With the new makeup of Congress, here are 5 senators to keep an eye on this session.

1. Rand Paul (R-Ky.)

Since entering the Senate in 2010, Paul has advocated severe cuts to foreign aid, including to Israel. However, it is not easy to win the Republican presidential nomination without showing sufficient support for one of the U.S.'s strongest allies.

In the first week of the new session, Paul introduced a bill to defund the Palestinian Authority until they withdraw their request to join the International Criminal Court, thus staying within his libertarian mindset, but also showing some solidarity with Israel.

Paul is also forgoing the big House-Senate Republican retreat to travel to some key presidential states, including New Hampshire. All signs point to a run in 2016, which will make his actions in Congress all the more interesting to watch.

2. Heidi Heitkamp (D-N.D.)

The junior senator from North Dakota represents one of the more conservative states in the nation, which Romney also carried in the 2012 election. Seen as an independent voice in the Senate, she is apparently already on McConnell’s watch list as a crucial swing vote when Republicans might need to overcome filibusters.

North Dakota’s Republican senior senator, John Hoeven, already introduced a bill to authorize the Keystone XL pipeline on the first day of the new session, and Heitkamp has gone against her party to favor the project. She is widely expected to vote for this new round of authorization, despite the fact that Obama is likely to veto any bill that is passed.

Current rumors swirling about her hopes for another gubernatorial run in 2016 may impact her desire to move toward the right in the historically red state. This may even end up making her an even greater ally for independent-minded Democrats in the 114th Congress.

3. Bernie Sanders (I-Vt.)

One of only two independents, Sanders has served in various positions representing Vermont, from mayor of its largest city, Burlington, to serving in the U.S. House, and finally the Senate. Now, there are widespread rumors that he may make a run for the presidency in 2016.

Although Sanders is recognized as an independent, he is a self-declared socialist who will likely represent hard-left positions in Congress in order to fight what he calls the “not-so-slow” decline of the middle class. What he will do about it is worth watching.

One place to follow carefully will be the Senate Budget Committee. While Republican U.S. Sen. Mike Enzi of Wyoming is the new chair of the committee and will surely clash with the Vermont senator, Sanders has already said that he would like to see the U.S. budget “reflect the needs of working class families and not Wall Street and the top 1%.”

4. Angus King (I-Maine.)

With the 114th Congress, King will serve on the energy committee, which he hopes to use to “push for the use of cleaner energy and the protection of natural resources.” King has a particular interest in the topic after starting a wind power company in the early 2000s.

King also is deeply critical of the CIA’s torture methods during the Bush administration and serves on the intelligence committee, where he will now have some jurisdiction over how to grapple with the legacy of the brutal treatment. Among other actions, King voted to declassify the report to the general public in April 2014. He is now part of the effort to deal with the fallout from the revelations, which he said showed “fundamental flaws in the agency’s detention and interrogation program.”

5. Michael Bennet (D-Colo.)

As the senior senator from Colorado, Bennet came into the Senate by gubernatorial appointment to replace Ken Salazar in 2009. He did, however, win his own election in 2010 and is expected to run again in 2016.

Bennet, a former school superintendent, prides himself on education reform, particularly in overhauling the No Child Left Behind Act from the Bush administration. While Bennet is fairly liberal on many key issues, including health care and immigration, Colorado is a fairly moderate state and his positions moderate to respond to his constituents.

More importantly, Bennet and his state’s junior senator, Republican Cory Gardner, may have the best chance at collaboration. Colorado frequently swings between parties, as both of their elections show, and therefore the two senators have an interest in working together for the state. Both men also support the construction of the Keystone XL pipeline and have a similar approach to energy alternatives in their state, which includes supporting Colorado’s important liquid natural gas industry.