Republicans have won the majority in the Senate, flipping the body after four years of Democratic control.

This was the predicted outcome, given how vulnerable Democrats were this cycle: While they defended nine contested seats, Republicans only defended three. Republicans successfully defeated key states like West Virginia and Ohio and held off unexpected competitive challenges in places like Nebraska and Texas.

The Republican victories come as former President Donald Trump is ahead in the election and several swing states remain to be contested. As of 2 a.m. ET, the presidential race has not yet been called for either candidate, but early results appear to point to an advantage for Trump as Vice President Kamala Harris' plausible chances of victory narrow.

In their campaigns, Republican Senate candidates relied heavily on criticism of Democrats' economic policies as many voters continued to struggle with inflation and the high cost of living. They also continued to stoke fears about immigration, arguing that only they could offer solutions to the 2023 surge in border crossings. Lacking control in the Senate, Republican candidates were able to capitalize on overall anti-incumbent sentiment — and current discontent — running high as they campaigned to take back certain seats.

Republican successes could have significant implications for a potential Trump or Harris administration. If Trump wins, the Republican Senate would effectively give him a blank check for the appointment and allow him to repopulate the courts with his judges. Depending on the outcome of the House elections, a Republican Senate could also allow a potential Trump administration to pursue policy priorities such as rolling back the Affordable Care Act (ACA) and renewing corporate tax cuts. If Harris wins, the Senate could obstruct key justice officials and block their legislative goals.

What Republican Senate Control Could Mean

What role the Senate will play in the next few years will depend largely on who wins the presidential race.

The last Trump presidency was ultimately an example of what happens when both the White House and the Senate are occupied by Republicans.

In this scenario, Trump was able to quickly develop his judges and reshape the District Court and Supreme Court with conservative decisions. In total, Trump was able to confirm 234 justices, including the three now on the Supreme Court who proved instrumental in the ouster Roe v. Wade.

Similarly, Trump has faced little backlash or accountability for his rhetoric or policy decisions throughout his time in office, including attempts to impose a ban on Muslims entering the country or shutting down the government to block funding for a wall along the U.S.-Mexico border make possible. Although some Republican senators spoke out, few actually voiced their opposition to Trump or questioned his actions. For example, when Trump was impeached for his role in inciting the January 6 insurrection, only seven Republicans voted to convict him – the rest voted to acquit him.

If Republicans retain control of the House, a GOP Congress could also help Trump advance his legislative agenda.

Trump has focused more on executive actions he would like to take (e.g. on tariffs, immigration and international relations) than on a congressional agenda. However, Republicans have long expressed interest in restricting access to the ACA. One issue lawmakers will address next year is the expiration of ACA premium subsidies, Stat reports. House Speaker Mike Johnson has already emphasized that he is also interested in comprehensive “reform” of the health care law.

The tax cuts that Republicans passed in 2017 are also up for renewal and will be another issue for lawmakers to address in the next Congress. Trump has proposed a cut in the corporate tax rate and has also introduced some income tax cuts. Regardless of whether they win the House, Republicans in the Senate are likely to push for these cuts. And Republicans could also push for an expansion of oil and gas drilling leases, which Democrats had previously limited.

Senate Republicans have already signaled that they plan to be as obstructive as possible when dealing with a Harris administration.

Notably, both Sens. John Thune (R-SD) and John Cornyn (R-TX), two likely successors to Senate Minority Leader Mitch McConnell, told CNN that they weren't sure whether they would vote for one Potential Harris would vote for Supreme Court nominations. With the majority, the GOP can try to block the nomination of a Harris justice, much as it once did with former President Barack Obama's Supreme Court nominee Merrick Garland and some of his lower court nominees. In Garland's case, the GOP successfully refused to ever hold a confirmation hearing or vote for him — and was able to prevent him from taking the bench.

They could do the same for other cabinet positions, and they could also block further development of legislation. Harris pushed hard to work to pass policies that require congressional approval, including comprehensive immigration and abortion reform. These policy goals are unlikely to become reality in a Senate controlled by the Republican Party.

Regardless of whether Trump or Harris are in the White House, you can expect the upper house to play a major role in helping or hindering their efforts.