John McCain’s political legacy is likely to be the subject of conversation and reflection for quite a while after his death on Saturday. But his Arizona Senate seat probably won’t stay vacant for long. Gov. Doug Ducey of Arizona will appoint McCain’s replacement, and the Republican can select someone as soon as he wants. I expect him to land on a replacement within the next two weeks, maybe even sooner (it has been clear for months that McCain was close to death and might need to be replaced). Ducey’s choice is likely to be sworn into the Senate within a few days of being chosen — and then become a fairly reliable vote for initiatives backed by President Trump and Senate Majority Leader Mitch McConnell.

So what kind of politician should we expect Ducey to land on for McCain’s replacement, and what will that choice mean for the future of the Senate, President Trump’s Supreme Court nomination and national politics in general?

Who will Ducey pick?

Some (journalists and pundit types) have floated the idea of Ducey picking McCain’s widow, Cindy McCain, for the seat. According to the Arizona Republic, the past few months, Cindy McCain, 64, has been speaking on behalf of the senator at events he could not attend because of his health. We don’t know much about Cindy McCain’s political views. And that uncertainty is why I don’t expect Ducey to choose her. I think Ducey is likely to pick someone who is a reliable Republican vote — picking someone without a clear record on many issues is an inherent risk.

Ducey is not a McCain-style Republican himself and has no incentive to appoint someone who occasionally breaks with the GOP’s priorities, as McCain did. To sum up the governor’s politics briefly: Ducey is a fairly traditional Republican on policy (he is a strong backer of cutting taxes, limiting abortion rights and expanding gun rights), doesn’t have a record of bucking his party on major issues and has built some fairly strong ties to President Trump and the White House. He seems to have presidential aspirations, so choosing a replacement for McCain who is liked by key party activists and donors could help him there.

Ducey is up for re-election this year, however, which means that his choice could have electoral implications for himself. But Arizona leans red and Ducey is favored, so I don’t think the governor will feel pressured to assuage moderate voters by selecting a senator who is more liberal than the governor himself.

So let’s assume a fairly traditional conservative pick. The big question is whether Ducey will go with someone who will act as a caretaker for the seat (Jon Kyl, the longtime Arizona senator who retired in 2013, for example) or someone who will want to stay in the seat long term. (That person would have to run in a special election in November 2020, to serve out the remainder of McCain’s term, and then again in 2022 for a full six-year term.)

I expect Ducey to pick a caretaker because the Arizona GOP is divided between a more establishment wing (Ducey) and a more tea party one (former sheriff Joe Arpaio). It would be smart politics for Ducey to avoid irritating one of those groups by choosing someone not seeking a long-term Senate career.

What will the new Arizona senator mean for national politics?

A new occupant of McCain’s seat is good news for McConnell, Trump and Republicans who want the party to largely follow the edicts of those two GOP leaders. McCain was largely absent from public life while he was receiving treatment for brain cancer, and during that time, the Senate was split 50-49 in favor of the GOP. That meant one Republican defection could kill any bill. With 51 active Republicans, one defection still left room for Vice President Mike Pence to cast a tie-breaking vote in favor of McConnell and the president. With 50, Pence’s vote isn’t enough as long as one Republican sides with the opposition.

With the addition of a reliable McConnell ally, the Senate’s partisan breakdown returns to 51-49, giving Republican leadership some breathing room. Retiring Sen. Jeff Flake of Arizona, a Trump critic who occasionally bucks party leadership, will have less power to stall Senate GOP initiatives. That could help the party get more federal judges appointed, a big priority for Trump and McConnell. (I don’t think the return to full strength in the Senate will mean much for other issues, because the Republicans aren’t really trying to push through major initiatives before the midterms.)

What about the Kavanaugh nomination?

I don’t think a new senator makes a big difference here. In terms of pure numbers, yes, the Republicans can now afford to lose the vote of one senator and still confirm Brett Kavanaugh, Trump’s appointee to replace retiring Supreme Court Justice Anthony Kennedy. But there has been little evidence that any Republican senator is willing to oppose the Kavanaugh nomination, so he probably already has the 50 votes required. (So let’s say that Cindy McCain was appointed and, for some reason, strongly opposed Kavanaugh — something I doubt would happen. But even then, there would likely be 50 other Republican Senate votes, and Pence could cast the 51st.)

Also, there is a strong chance that some Democrats, like Indiana’s Joe Donnelly and West Virginia’s Joe Manchin, will vote for the Supreme Court nominee. So while the confirmation of Kavanaugh is slightly easier with a replacement in McCain’s seat, I think the outcome of that process was already clear — barring some major discoveries about Kavanaugh.

Any other ways the new senator could have an impact?

A new senator from Arizona could contribute to the Republicans having a much more manageable/party-line caucus if they retain control of the Senate in 2019.

In 2017, when McCain was on Capitol Hill regularly, he was not a reliable vote for Trump and McConnell (according to FiveThirtyEight’s Trump score, McCain votes in line with the president’s position at the fifth-lowest rate of any Republican senator). And the 2018 Senate electoral map is favorable to the GOP. So the Republicans could end up with 52 or more seats in January 2019, but without some of the most anti-Trump GOP senators — McCain, Flake and Tennessee’s Bob Corker, who is retiring too, will all be gone. That means the Republicans would have a majority of about the same size as it is now, but with members who are much more likely to be loyal to the Trump/McConnell agenda.

If the Republicans have 52 seats in that scenario, GOP Sens. Susan Collins of Maine and Lisa Murkowski of Alaska, major swing votes in 2017 and 2018, would be disempowered. The GOP would be able to pass legislation without their support, which would allow Trump to appoint judicial and executive branch nominees who are more in line with his policy views.