The STOXX 600 closed 0.1 percent lower, marking a five-day loss of almost 1 percent. Britain's FTSE <.FTSE> slipped 0.1 percent and posted a weekly decline of 1.9 percent. European markets closed before Trump's inauguration speech.
The pan-European index has gained around 7 percent over the last two months, but it has slipped from its early January peak amid concerns Trump may struggle to deliver on his stimulus promises.
“I think markets now are attuned to expecting the unexpected, but by definition it means that there can be surprises along the way,” Geoffrey Yu, Head of UK Chief Investment Office at UBS Wealth Management, said.
"This is a very unorthodox presidency, so we just won’t know and markets didn’t pre-position themselves for tweets, either.”
The broader market was weakened by some disappointing earnings updates, although merger and acquisition talk helped support the telecoms sector.
British pharma stock AstraZeneca (>> AstraZeneca plc) was 3.4 percent weaker, the biggest faller on the FTSE 100 index after rival Bristol-Myers Squibb Co (>> Bristol-Myers Squibb Co) decided not to seek accelerated U.S. approval for a combination of two immunotherapy drugs as an initial treatment for lung cancer.
The fall weighed on Europe's health care index <.SXDP>, down 0.8 percent.
Danish insurer Tryg (>> Tryg A/S) was also among the biggest STOXX losers, down 2.9 percent after its fourth-quarter profit missed expectations.
Britain's AA (>> AA PLC) also dropped, falling 6.2 percent on worries about costs.
Energy stocks were among the biggest gainers, however, with shares in Subsea 7 (>> Subsea 7 SA), Amec Foster Wheeler (>> Amec Foster Wheeler PLC) and SBM Offshore (>> SBM Offshore) all rising between 4.7 percent to 5.4 percent.
Amec Foster Wheeler benefited from a SocGen upgrade to "buy", citing the potential for the oil company's shares to re-rate.
TDC (>> TDC A/S) also rose, up 3.9 percent after a report in Dagens Industri said telecom operator Telia (>> TeliaSonera AB) was considering a bid for the Danish company, which is itself exploring a takeover of Swedish cable TV company Com Hem.
Telia and TDC both declined to comment on the report.
Gains in TDC drove Europe's STOXX telco index <.SXKP> up 0.6 percent.
Banks <.SX7P> were also firmer, with Commerzbank (>> Commerzbank AG) rising 2.8 percent after a price target upgrade from analysts at Deutsche Bank.
Shares in Italy's UBI Banca (>> Unione di Banche Italiane SpA) were the biggest fallers among the banking stocks, ending 2.2 percent lower after DBRS cut the trend on UBI Banca's debt ratings to negative following its acquisition of three banks.
(Corrects Yu's title in paragraph 4)
(Reporting by Kit Rees and Danilo Masoni; Editing by Alison Williams)
By Kit Rees and Danilo Masoni
Stocks treated in this article : SBM Offshore
, Bristol-Myers Squibb Co
, Unione di Banche Italiane SpA
, TDC A/S
, Tryg A/S
, Subsea 7 SA
, AstraZeneca plc
, Commerzbank AG
, AA PLC
, Amec Foster Wheeler PLC
, TeliaSonera AB