The cause?

A presumptive presidential nominee whose standing with key voting blocs -- and in key battleground states -- is in decline and who has failed to deliver on frequent promises to follow a somewhat more traditional campaign course.

The worries were deepening even before the Orlando nightclub tragedy and have grown more profound since, as veteran Republican officials in Washington and around the country talk not only about Donald Trump's recent troubles as a candidate but the potential, in their view, for a damaging "Trump effect" on other Republican candidates.

A couple of important caveats: it is June -- the election is more than 140 days away and every candidate has bad stretches -- plus many of the complaints about Trump and his team come from people who were skeptical of Trump from day one.

Still, the jitters are real -- as are the reasons for them. Here are five reasons for the GOP angst:

Pre-Orlando: Clear signs the judge attacks were taking a toll

As last week came to a close, before the Orlando mass murder took over the news, Republicans involved in key Senate races were sounding the alarm about the impact of Trump's attacks on the federal judge overseeing the Trump University fraud case. GOP strategists and GOP allies working the Senate races in New Hampshire, Pennsylvania, Ohio and Wisconsin all reported a drop in Trump's standing. In Ohio, according to a well-placed GOP source, Trump fell from a statistical dead heat with Hillary Clinton to minus 10 points.

Each of those Senate races has its unique dynamics, and some of the incumbents are more vulnerable than others. So far, though, the strategists say there is no automatic "Trump effect," meaning the incumbents do not necessarily drop when trump does.

But they are worried nonetheless, readily conceding that if Trump loses their state by more than 3 to 5 five points it will be difficult for the incumbent not to get swept away. A second seasoned GOP insider tells CNN that Senate Majority Leader Mitch McConnell, in a brief conversation with Trump last weekend, made the point that Trump's trajectory had a direct connection to Senate GOP hopes of protecting their majority.

The $$ conversation is not going Trump's way at the moment

Some Republicans are actually quite happy about this: Top allies of McConnell and House Speaker Paul Ryan have made clear their priority is protecting the congressional majorities, and that they have little faith any money sent Trump's way will be spent on anything other than helping Trump. 2012 GOP nominee Mitt Romney is also in the "Never Trump" camp and has made clear to his deep fundraising network he thinks it best that money be directed to those who are focusing on House and Senate races.

Not that Trump isn't making some inroads. At a big fundraising meeting in New York last week, there were mixed opinions. Several GOP donors left impressed and were more open to the unorthodox style of the party's presumptive nominee. Others bemoaned a lack of discipline and airing worries that Trump and his team grossly underestimate the amount of resources they will need to be competitive.

Several participants said it was made clear at the meeting that it will take time to raise significant resources for Trump and Republican National Committee joint efforts, and that a short-term infusion from the candidate himself would be helpful. But there was no commitment, and many of those on hand barely made it outside of the Four Seasons meeting before chatting among themselves about their bets that Trump, for all his worth on paper, is not awash in liquid assets.

Team Clinton looks deeper -- and gets begrudging credit from GOP strategists

Most Republican strategists are privately offering begrudging praise of the Clinton campaign of late, suggesting Clinton and her team -- as well as their allies -- have learned some key lessons from the GOP primary season. These strategists note how the Clinton campaign is taking Trump seriously from day one, something most of his primary opponents did not.

As examples, they cite the aggressive debates with Trump every news cycle -- and on virtually every platform. Plus, it is not lost on Republicans that Clinton is getting help from a deep Democratic bench: President Barack Obama and Michelle Obama, former President Bill Clinton, Vice President Joe Biden, Massachusetts Sen. Elizabeth Warren and, soon most believe, primary rival Vermont Sen. Bernie Sanders.

In contrast, seemingly every day senior Republicans are making clear they disagree with Trump on one issue or another, or simply refusing to answer questions about him. Trump says he doesn't think he needs a traditional surrogate operation, just as he argues he doesn't need a traditional fundraising apparatus. But most GOP strategists not aligned with Trump take issue, noting the advantage Clinton will have sending Democratic Party stalwarts into key battleground states.

Trump's Orlando response adds to the focus and discipline worries

Complaints about a lack of focus and discipline from Trump are hardly new and even many of those who make these complaints concede his approach was quite successful in the GOP primaries. But the attacks on the judge brought these worries to a near panic level, and Trump's response to the Orlando massacre have only reinforced them.

Most Republicans believe a strong case can be made: that Obama should have pressed more forcefully to leave a residual U.S. troop presence in Iraq; that his calling ISIS the "JV" at one point proves he was slow to understand the threat, and that Clinton's record on issues related to Syria and Libya offer opportunities to question her performance and judgment.

"But our candidate for president prefers innuendo and conspiracy theories," a Republican senator told CNN in a conversation Wednesday.

How deep is this worry? It was no accident that McConnell last week said publicly he preferred Trump stick to a script because it is clear he isn't well prepared on the issues. That senior Republicans now are forced to take issue with Trump's characterizations of Obama annoys them to no end. Again, Trump shrugs this off and says his critics are establishment Republicans and part of the problem. Those outside of Team Trump see chaos when it comes to trying to communicate a consistent Republican message in the fall.

The numbers don't lie and they do invite coup plotting

A new Bloomberg poll suggests a 12-point Hillary Clinton lead nationally.

Plus, the new ABC News/Washington Post survey shows seven in 10 Americans view Trump unfavorably.

Those and other numbers are behind talk inside Washington that Trump is losing the election even before he officially claims the GOP nomination.

Those numbers are also cited in the flurry of emails among those somehow hoping to block Trump from the trophy presentation in Cleveland. "Stop Trump" failed in the primaries. "Never Trump" could not find a credible conservative third-party challenger. Now "Dump Trump" forces are dreaming of a Cleveland convention coup.

Dont bet on it; these forces have a lousy track record so far, plus running unopposed at the end of the primary season gave Trump a whopping delegate lead. But talk of a coup does reinforce the notion of GOP chaos at a time the Democrats are coming together.

So is it possible the race is baked? Meaning that Trump's negatives are already too overwhelming to change things and win.

Don't bet on that either.

The clamoring for change and something different is off the charts, and Trump continues to lead Clinton significantly when voters are asked which candidate is more likely to shake things up in Washington.

Plus, she has high negatives, too, plus an ongoing federal investigation of the private email server she used while leading the State Department.

The GOP jitters are real, and for good reason.

But it is June. And a cycle where if we have learned anything, it should be to expect the unexpected.