In bizarre behavior which can only be indicative of election fraud, polls in 2018 midterm races proved nearly perfectly predictive in one set of races but entirely wrong in another. The results throw a monkey wrench into the argument that polls are simply unreliable. The polls were selectively reliable, proving accurate in predicting the GOP's retained hold on the US Senate, but massively unreliable when it came to the House of Representatives flip to blue, which gave Democrats control of the committees charged with investigation of the affairs of President Donald J. Trump. Control of the committees enable Democrats to open investigations and hold hearings with broad latitude.
Further, as has been constantly pointed out by critics of the US election system, present practices prevent any independent verification of election results. Because paper ballots cannot be accessed by the public except in recounts to which there are enormous hurdles, the vote counting system is entirely opaque.
In the hotly contested races for the House, ten poll averages proved wrong, even ones in which GOP candidates were as much as 4 points up. But in close Senate races, polls predicted winners with great accuracy, in 8 out of 10 races (one had polls tied.) One of the outlier races was the Senate race in Florida, where both sides have cried foul.
Following are the poll versus actual results in what were closely watched US House races, as compiled by Richard Charnin from poll averages at Real Clear Politics. The left-hand box is poll averages. The right box lists actual results. Note that in each case the poll predicts a Republican victory, but the Democrat won.
But in hotly contested Senate races, polls correctly predicted the winners in eight out of ten races, with all but one, Jon Tester, being Republican.
In an additional oddity in California, there was a significant Democratic "over-vote" in Orange County congressional elections. 300,000 more Democrats voted for the Democrats in the congressional races than voted for Democrat Gavin Newsom for governor. This constitutes a significant percentage of the ballots in Orange County.
Outgoing House Speaker Paul Ryan puzzled over the results in the California races for the House, saying: “We were only down 26 seats the night of the election and three weeks later, we lost basically every California race."
Election activists have long been pushing for transparency in elections, which would make it possible for citizens to independently verify vote-counting machine totals. One measure being pushed for is ballot image access, in which the little known about images which are taken by most modern optical scan vote-counting machines are publicly posted. Another measure is to end the over-use of mail-in ballots and "ballot harvesting," a California law which allows campaign workers to pick up and deliver mail-in ballots to polling places on behalf of voters.
Further reading: "How to Have Hack-Proof Elections in America, Easily, and Why Politicians are Against it"