(CNN) National Republicans are likely to have a significant advertising advantage in the fierce battle for control of the Senate, an edge that comes in spite of Donald Trump tilting what as already an unfavorable map for Senate Republicans further against them.

Almost all of the traditional Republican outside groups, ranging from the network organized by the billionaire Koch Brothers to the establishment-aligned Chamber of Commerce, have rebuked Trump and declined to spend their millions of dollars on his behalf. And that is paving the way for a torrent of spending on behalf of Republican Senate candidates, with national Republican groups poised to cross $155 million in general election advertising this cycle, according to groups' plans and a CNN analysis of CMAG/Kantar Media television and radio advertising records.

National Democrats, on the other hand, are only planning to air around $120 million worth of ads, a gap that though not insurmountable, will require Democratic challengers to do more with less to take back control of the upper chamber.

"A lot of people decided that the Senate races are equally important -- and in some cases, people have decided that they're more important," said Bob Pence, who was installed on Thursday as the National Republican Senatorial Committee's finance director. Donors have been attracted to the certainty of the Senate committees, in contrast to the unwieldy presidential race, Pence explained.

Strategists on both sides of the aisle caution that initial reservations can and almost always change as their fundraising spikes and plummets and their chosen candidates rise and fall. And Democrats are used to being outspent, given major donors' once reluctant embrace of big-money groups that have powered the Republican ticket in recent cycles.

Republicans this week continued to bolster their advertising lead, with groups tied to Senator Mitch McConnell and strategist Karl Rove promising another $1.5 million in time to boost Marco Rubio's reelection bid in Florida. The McConnell-Rove network outlined this month plans for about $40 million in fall advertising, and the Koch network has signaled that it will chip in another $30 million as part of its first round of television time.

Those two networks, which rely on both super PACs and nonprofit groups, which are not required to disclose their donors, have already aired more than $36 million in general election advertising for Republicans, and each group says they have spent even more than is seen in available records. And the Chamber of Commerce -- which spent more money than any other outside group in the 2014 midterms and has already spent nearly $13 million in November Senate races -- has yet to publicly purchase its fall time, meaning that the gap between Democrats and Republicans could swell even further.

Many Republican donors, dismayed that Trump trampled over their favored presidential candidates in the Republican primary, have voiced that they plan to reinvest their fortunes in these outside groups and essentially sit out of the presidential race. That's meant bigger warchests for Republican groups.

The ad wars are expected to play out primarily in five states: Ohio, Florida, Pennsylvania, New Hampshire and Wisconsin. The national Democrat vs. Republican figures do not include the ads of individual candidates or state-specific super PACs organized solely to support them, nor in the two competitive Democratic primaries in Maryland and Pennsylvania or the Republican ones in Indiana or Arizona.

But even with more national cash, Trump has undoubtedly made their task harder: More vulnerable Republicans from Mark Kirk in Illinois to Kelly Ayotte in New Hampshire have taken pains to distance themselves from their presumptive nominee, and Democrats are branding Republicans with Trump's imprimatur in states where he is expected to be a significant drag on downballot candidates.

"Donald Trump wants the Senate to delay filling the Supreme Court vacancy so he can choose the nominee next year," one ad from Senate Majority PAC in March went, extensively featuring Trump's remarks at a GOP presidential debate. "And Senator Kelly Ayotte is right there to help."

Democrats so far have remained competitive thanks to their party committee, which has not begun advertising but has pledged $50 million in fall advertising so far. That outpaces their Republican counterpart, the National Republican Senatorial Committee, which is so far investing only $28 million in fall races. Those initial placements are expected to grow substantially.

Senate Democrats' main outside group, the Harry Reid-backed Senate Majority PAC, is scheduled to air $45 million in the fall and has already aired more than $12 million in general election ad time.

"We're playing offense across the map in states where Republicans have increasingly narrow paths to victory," said Shirpal Shah, a spokesperson for the group. "No matter how much they spend, they won't be able to separate themselves from Donald Trump."

But as of now, those groups are largely alone.

While national Democratic groups have engaged in the Maryland and Pennsylvania Democratic primaries, the only other national group that has spent more than $2 million in general election advertising has been the National Resources Defense Council, which spent $4.8 million to boost Tammy Duckworth in Illinois, according to advertising records.

Other Democratic big-money mainstays have been quiet. NextGen Climate, a group funded by energy billionaire Tom Steyer, has not run a single television ad or purchase this cycle, instead channelings its funds to field and digital programs. And labor groups say they too have not yet reserved television time in key Senate races, though unions like AFSCME so far have spent almost $900,000 pillorying Rob Portman, the Republican incumbent in Ohio.

Some Democratic operatives stress that their investments are to arrive soon. But if sapping enthusiasm for Trump's campaign has emboldened big-money groups on the Republican side, Senate Democrats may be evidence of the opposite effect.

Hillary Clinton's super PAC is in the middle of a planned $120 million onslaught on Trump -- and it's only July.