FOR the first time in 17 years on Thursday, the holy trinity of major US stock indexes - the Dow Jones Industrial Average, the Standard & Poor's 500 and the Nasdaq Composite - all finished at record highs.
The Dow and S&P 500 had previously blown through their 1999-2000 summits in 2013 after first recovering them in 2007. But many investors thought the Nasdaq would never see the dizzy heights reached at the turn of the millennium again.
A surge for the biotech sector last July defied those prophecies - briefly, but this time, the Nasdaq's gains are more in sync with the broad market, driven not by the biotech stocks on the fringes of the Nasdaq, but the technology stocks at its core, companies that now also form the core of the blue-chip indexes. Microsoft, Apple, Amazon.com and Google's parent company Alphabet were among the sleeping giants which awoke after reporting resurgent earnings.
But are the gains any more sustainable than those last year? The rise of tech stocks is a sign that investors' appetite for risk is growing once more. But reminders of new Federal Reserve rate-hike plans, China's fading economic miracle, oil's slide and Britain's vote to leave the European Union could cause another flight into "safe havens" such as gold and bonds, as happened in 2015 and earlier this year.
One strategist predicted a run-up in stocks between now and the Fed's central banking conference in Jackson Hole, Wyoming in two weeks, which might then be followed by a rude awakening.
"Next thrust higher in risk assets will likely complete the rally from February lows as . . . 'greed' has replaced 'fear'," said strategists at brokerage Bank of America Merrill Lynch (BOAML) in a note to clients. The central bank's meeting could be a reminder of the hike plans, strategists warn.
A continuation of the rally in the coming sessions would represent a "mini-meltup in risk" as traders chase the momentum in tech stocks and elsewhere, according to the BOAML strategists.
Another sector that unexpectedly rose last week was retailers, which enjoyed a relief rally. While sales reports and layoff plans from Macy's, Kohl's and JCPenney were a far cry from their peaks, they were a lot better than investors had feared since they view the challenge from online competition in general and Amazon.com in particular as life-threatening to these companies.
The rally in the retailers' shares was prompted, in part, by what amounted to a survival strategy outlined by Macy's. Another catalyst was Walmart's US$3 billion purchase of an online retailer - a tacit admission from the world's largest retailer that it had some catching up to do with Amazon.com.
Only one group of bricks-and-mortar retailers has thrived in the Amazon age - deep discounters. Some of those chains, such as TJX, will report earnings this week.
Similarly, analysts at brokerage Nomura Securities argued media stocks have returned to favour not because of their growth prospects but because the pace of subscriber losses has not been as rapid as investors feared. Most analysts say cable companies such as Comcast and Charter Communications, both of which reported surprisingly strong earnings, will eventually see customers flee to cheaper online television, in a trend that's known as "cord cutting".
This week will see another tug of war between bulls and bears in the oil market. Last week, oil futures tested lows around US$40 per barrel level again only to finish at a three-week high around US$44. The bears say the relentless rise in US inventories is bound to crush prices again, eventually. There's a sense that most US drillers have put operations on temporary hiatus rather than permanently shutting in wells or quitting exploration. Until such time as the "wildcatters" on US shale fields are shaken out once and for all, the bears argue, the US glut will quickly rebuild.
The bulls point to statements from Saudi Arabian officials indicating that they will push for a freeze in production levels for members of the Organization of the Petroleum Exporting Countries at the next meeting in September.
Energy policy in the United States, another key factor in global supply, could well change with the new presidential administration.
Last week saw US Democratic presidential candidate Hillary Clinton stretch her lead over rival Donald Trump in opinion polls nationwide. Time magazine reported that Republican Party elders were so frustrated with Mr Trump's slump that they had threatened to yank support for him.
Oliver Pursche, chief executive of broker dealer Bruderman Brothers, warned against writing off Mr Trump's chances so early, however.
"An awful lot can happen between now and November 7," Mr Pursche said. Some polls in the immediate wake of the Republican convention had shown Mr Trump leading. The success of the Democratic convention and subsequent gaffes from Mr Trump have since decimated his standing in polls. A Clinton scandal or some other shift in the political landscape could swing voters back in Mr Trump's direction, Mr Pursche said.
"This is where everybody is uneasy neither one of these candidates have a high favourabilty rating . . . to the contrary these are two of the most unpopular candidates in the history of the US."
In other words, the summer rally should continue this week, but don't expect the autumn to be plain sailing.