Four cases that could re-shape the country will be heard when the Supreme Court meets this term without Justice Antonin Scalia. Scalia consistently expressed conservative views when reviewing court cases. (Claritza Jimenez/The Washington Post)

As the Senate returns to work Monday for the first time since Supreme Court Justice Antonin Scalia's death, Senate Republicans have a major decision on their hands.

Do they consider President Obama's to-be-determined nominee to fill Scalia's seat and risk upsetting their base? Do they try to block consideration of Obama's nominee for a whole year and risk upsetting a broader pool of voters? Or do they aim for something in the middle?

It's a tough decision with potentially major consequences at the ballot box -- not to mention the future of the court itself. As such, Senate Republicans are starting to fall into one of five groups about what to do and how to do it. Most of these categories, we should point out, really are different ways to say no to Obama's nominee. The key disagreement is in how to go about it, strategically and politically.

Here are the five factions:

1. It's not fair to the people to consider a nominee now

The argument here is that the people should decide who sits on the court. In November, Americans will pick the next president; in January, the next president should pick the next Supreme Court justice.

It's a popular line of thinking among the GOP base. A recent NBC/Wall Street Journal poll found 81 percent of Republicans think the Senate should wait to vote on a nominee until next year. In the Senate, supporters of this argument make up some of the chamber's most conservative members. Sen. Ted Cruz (R-Tex.) has already threatened a filibuster of any Obama nominee. Conservative activist group Judicial Crisis Network is also running ads in states with vulnerable Senate Republicans who have publicly said the Senate should wait for the next president to vote on a nominee.

Senate Majority Leader Mitch McConnell (R-Ky.) is in line with conservatives here, too. Hours after Scalia's death was announced, McConnell sent out a statement saying it would be imprudent to consider the nominee of lame-duck president. The head of the Senate committee that would hold hearings on Obama's pick has closed the door shut as well. Sen. Chuck Grassley (R-Iowa) and McConnell co-wrote an op-ed in The Washington Post that read:

It is today the American people, rather than a lame-duck president whose priorities and policies they just rejected in the most recent national election, who should be afforded the opportunity to replace Justice Scalia.

2. It's not fair to the Supreme Court

The political stakes tied to this vacancy have perhaps never been higher. Control of the Senate, White House and ideological tilt of the Supreme Court are up for grabs. What happens most likely rests on the outcome of this year's wide-open presidential election. In other words: This vacancy is inextricably linked to politics right now.

Some Senate Republicans say that's reason enough to wait until next year, when things settle down. They don't think any nominee would  get a fair hearing right now and question whether an inflamed Senate would give one.

Sen. Orrin Hatch (R-Utah), Senate Republicans' most senior member and former chair of the committee that would head confirmation hearings, spoke with The Post's Mike DeBonis and Juliet Eilperin about this:

He worries that a political spectacle amid a presidential race could be “demeaning” to the nominee, the Senate and the panel’s reputation for conducting fair and serious work.

"We are in the midst of one of the most obnoxious, terrible presidential campaigns that I’ve ever seen. I don’t want to see the courts be smeared by being in the middle of the process.”

3. Democrats brought this upon themselves

Here's another way of saying "no" to Obama's pick. Sure, the Senate should consider qualified picks -- traditionally, politics isn't even supposed to factor in these nominations and confirmation processes (though it almost always does). But in recent years, Senate Democrats and Obama have subverted the rules on Senate confirmation of judicial appointments. So why should Republicans play along with the rules this time?

Sen. Lindsey Graham (R-S.C.) is squarely in this camp. Graham is referring to Senate Democrats' 2013 change of Senate rules that require only a simply majority of senators to approve lower-court judicial nominees (the Supreme Court is not included in this). The rules change makes it easier for the party in the majority to approve the president's judicial nominations and harder for the party in the minority to oppose them.

"You’re leading the effort to turn the rules upside down, to pack the [Supreme] Court," Graham told The Post's Eilperin and Paul Kane. "There will be consequences, and I’ll find it very hard for me” to support a nominee now that “we are inside of a year” before the next president’s swearing-in.

4. Let's at least look like we're open to a nominee

The average Supreme Court confirmation process takes 75 to 90 days; Republicans will have to explain to the American people why they should block Obama's nominee for the next year.

Some junior senators, like Dean Heller (R-Nev.) and Thom Tillis (R-N.C.), think that's going to be a hard case to make. Senate Republicans risk handing Democrats a potentially politically damaging election-year attack -- that they are needlessly obstructing justice -- if they don't even consider Obama's nominee for an entire year.

Republicans will "fall into the trap of being obstructionist" if they go down that path, Tillis warned.

Besides, allowing hearings to go forward doesn't mean a nominee will actually be approved. Because of Cruz's threatened filibuster, 14 Republicans would need to join all 46 Democrats for that to happen. That's very unlikely to happen.

"The chances of approving a new nominee are slim," Heller said, "but Nevadans should have a voice in this process."

5. It's the Senate's duty to consider a nominee in good faith

This group of Republicans argue that politics really shouldn't enter the confirmation process at all. What Senate Republicans should do is written right there in the Constitution: Article II, Section 2: “[The President] shall nominate, and by and with the Advice and Consent of the Senate, shall appoint … Judges of the Supreme Court.”

Notably, though, the only people who are publicly arguing this now are more moderate Republicans who aren't in the Senate anymore.

"I can understand their reluctance given the controversy that surrounds all of the debate that has already occurred,” said Richard Lugar, a former senator from Indiana who lost to a conservative challenger in 2012, according to the New York Times' Carl Hulse. “But that is not sufficient reason to forgo your duty.”

Olympia Snowe, a former Republican senator from Maine, echoed Lugar's comments to Hulse: "I believe that the process should go forward and be given a good-faith effort — and ultimately people will come to their own decision on a vote on a nominee."