Alabama may have just elected its first Democratic senator in 25 years, but the legislators in the chamber who feel most emboldened may sit on the Republican side of the aisle. By narrowing the Republican majority, Doug Jones’s arrival further empowers Republicans who are willing to break with the party to kill or force changes to legislation and block nominations that they disagree with.

Jones’s election means that the Democrats go from 48 members to 49. That makes for a very large Senate minority, but one that Republicans can still override on legislation that only requires a simple majority to pass — like judicial nominations and bills that go through the reconciliation process. (The reconciliation process can only be used on fiscal issues, such as tax reform and the Obamacare repeals that the Senate considered earlier this year.) So Jones himself is not likely to be the swing senator. But now any two Republicans — not three, like before Jones was elected — can swing a vote against the GOP in the Senate.

The senators to watch: Well, there have been six instances this year in which a 50-50 Senate tally left Vice President Mike Pence to cast the tie-breaking vote. He has voted with the majority of Republicans all six times, allowing those provisions to pass.

In five of those six instances (all but one that rolled back a regulation created by the Consumer Financial Protection Bureau), the two Republican “no” votes were Maine’s Susan Collins and Alaska’s Lisa Murkowski. This is not surprising. Both senators are among the five Republicans who most often break with the Trump administration’s position according to FiveThirtyEight’s Trump Score. (Collins is the GOP senator who votes against Republicans most often.) And of course, Collins and Murkowski were two key opponents of the GOP’s push to repeal Obamacare.

Once Jones is seated in the Senate (which could happen late this month or in early January) and the GOP is down to a 51-person majority, Republicans can afford to have Collins or Murkowski vote against a bill, but not both. That pair can tank legislation if they both join with the 49 Democrats in the Senate. Think about how a 49th Democrat would have changed, say, the debate on Obamacare repeal, which was voted down only because Arizona’s John McCain emerged, in a surprise, to join Collins and Murkowski in voting against it.

Also keep an eye on the possibility of Collins or Murkowski joining with Tennessee’s Bob Corker or Arizona’s Jeff Flake or McCain, the anti-Trump trio that has more political freedom than most members because none of them are likely to face Republican voters again. (Corker and Flake are retiring in 2018, and McCain has been diagnosed with brain cancer.)

In addition, unique coalitions may arise because of the ways that specific issues affect a certain constituency. For example, two GOP senators from the same state can now take down legislation by allying with the Democrats. Or senators Mike Lee of Utah and Rand Paul of Kentucky, who are both deeply conservative and occasionally aligned, might join together to block something.

The issues where Jones won’t have much impact: This new dynamic probably won’t affect the most pressing matter before the body — tax reform. Congressional Republicans are trying to push their tax legislation through before Jones is sworn in and have discussed scheduling a final vote next week. With Republican Sen. Luther Strange still representing Alabama in the meantime, Republicans can afford two “no” votes on the tax bill and still pass it. Corker right now seems to be the only GOP senator who’s very likely to oppose the legislation.

In theory, Jones does cause some challenges on taxes. Republicans now face intense time pressure to pass the bill before Jones is installed. Moving quickly on a bill this complicated is difficult under any circumstances, and now some of the members who have reservations — such as Florida’s Marco Rubio, along with Flake and Collins — might join with Corker to stall the legislation until Jones arrives. Once Jones is seated, the Republicans will have exactly 50 senators who back this bill. That would give every individual member huge leverage to demand concessions that favor their constituents or agenda. As yet, though, there have been no signs that these reluctant Republicans will stall the bill until Jones is seated.

Jones is unlikely to have a dramatic impact on other policies, either. Remember, most legislation in the Senate can be stopped via a filibuster, which can be sustained with just 40 senators, meaning Democrats have a lot of power already.

The issue where Jones really matters: Both federal judgeships and posts in the executive branch can be approved with just 51 votes (50 senators plus Pence), so this is where having one fewer Republican senator could have a major impact.

The Senate has not yet voted down any high-profile Trump nominees — but that is not because Republican senators always back Trump’s selections. In February, Trump’s scandal-plagued nominee for labor secretary, Andrew Puzder, withdrew after several Senate Republicans signaled that they would vote against his confirmation. Betsy DeVos wouldn’t have become secretary of education without Pence’s tie-breaking vote. This week, two of the Trump administration’s nominees for federal district judgeships withdrew after it became clear that they were not likely to be confirmed by the Senate. With Jones in the Senate, I expect to see more instances where the Trump administration considers nominating someone but pulls back because it is not clear that person can be confirmed, or nominates someone but then withdraws the nomination after a couple of GOP senators say that they are not on board.

So it will be even harder for Trump to get people confirmed, particularly more controversial figures like DeVos. McCain, Corker and Flake, for instance, all have long resumes on foreign affairs and could well try to block whoever Trump nominates to replace Rex Tillerson, should the secretary of state step down in the next few months as expected. There are rumors that CIA Director Mike Pompeo could be tapped for the role, which would leave open another key position that can’t be filled without the Senate’s approval.

So Jones, who has fairly traditional Democratic stands on most issues, will come to Washington with great fanfare after his surprising election win. But he is unlikely to be in the center of the action on Capitol Hill. The senators to watch will be the same ones we’ve been following all year. Collins and Murkowski were already some of the most influential people in Washington. Now, they have even more power.