– Republicans’ chances of holding the U.S. Senate are improving considerably, thanks to Hillary Clinton’s sliding popularity, strong campaigns by Republican candidates and a GOP fundraising surge.

Just a few months ago, Republicans were fretting that a backlash against their presidential candidate, Donald Trump, could cost them the Senate. Now, two races Democrats have long targeted — Ohio and Florida — have started to slip away, as have Arizona and Iowa, where incumbent Republicans John McCain and Charles Grassley have built double-digit leads.

“The now-tight presidential race suggests that perhaps Clinton could pull off a narrow victory that still allows the GOP to hold the Senate,” wrote Larry Sabato, Kyle Kondik and Geoffrey Skelley of the University of Virginia Center for Politics as they moved four Senate races in the Republicans’ direction.

The shift marks a reversal for Senate Democrats, who have gone from hoping for an anti-Trump electoral wave to insisting that their darkening poll numbers aren’t accurate. Senate Democrats also say that a big fundraising haul for Republicans is to blame.

“The big Republican donors that give dark money … they’re panicky about Donald Trump, so they’re all in with Mitch McConnell and Republican senators,” Sen. Claire McCaskill, D-Mo., said in an interview last week, referring to the Senate majority leader. “We don’t have as many of those types that have real huge money and can give lots of money. The ones that we have are also panicked about Donald Trump, and they’re giving to Hillary Clinton.”

To be sure, there are bright spots for the Democrats, too: A poll over the weekend showed Republican Sen. Pat Toomey trailing Katie McGinty by 5 points in Pennsylvania, and Democratic challengers have led narrowly in some polls in North Carolina and Missouri.

Democrats still have far more pick-up opportunities than Republicans, and a swing in their favor of a few points could still net them several more seats than the four they need to win the majority if Clinton wins the White House.

Two groups allied with McConnell, the Senate Leadership Fund and One Nation, reported raising $42.4 million in August, with the leadership fund deploying about $60 million to battleground states this month. That includes $15.8 million to New Hampshire, where Republican Sen. Kelly Ayotte faces a tough race against Democratic Gov. Maggie ­Hassan, according to a spokesman for the groups, Ian Prior.

The One Nation issue ad group also spent about $25 million through August.

The Center for Responsive Politics, which tracks outside group ad spending, counted $30 million for Sen. Rob Portman, R-Ohio — almost all of it in ads attacking Democrat Ted Strickland — nearly doubling the amount spent by outside groups backing Strickland.

And groups linked to businessmen and prolific Republican donors Charles and David Koch have spent more than $25 million in Senate battlegrounds so far.

“I think it comes down to the money,” said Sen. Dick Durbin, D-Ill., who called the money flowing from the Senate Leadership Fund into Republican coffers in states like New Hampshire, where Ayotte has a narrow lead in recent polls, “mind-boggling.”

Both parties’ leaders have been browbeating their colleagues to pony up more of their own cash, and senators have responded with extra millions on both sides of the aisle in recent weeks.

Senate Minority Leader Harry Reid has repeatedly dismissed polls showing improving numbers for Trump and Senate Republicans and maintained that Democrats will still take back the Senate.

“I don’t buy your silliness with your $500 polls you buy overnight,” Reid said last week when he was asked by reporters about polls. “You only do it to generate some news.”

Reid insisted that Republican Rep. Joe Heck would lose to Democrat Catherine Cortez Masto in the battle to replace the retiring Reid in Nevada — the one Democratic seat in danger of flipping to the GOP.

Democrats have made a number of seats competitive that weren’t expected to be, including North Carolina, where Republican Sen. Richard Burr is facing off against Democrat Deborah Ross, and Missouri, where Republican Sen. Roy Blunt is facing Democrat Jason Kander.

Meanwhile, Democrat Evan Bayh’s lead in Indiana over Republican Rep. Todd Young has eroded badly.