BRUSSELS — Russia could pose a credible security threat to the European Union by the end of the decade and defense industries in Europe and Ukraine must be ramped up within five years in preparation, Danish Prime Minister Mette Frederiksen warned on Tuesday. In a speech to the European Parliament marking the launch of Denmark’s six-month term as holder of the EU presidency , Frederiksen lamented that “cutting our defense spending in the past 30 years was a huge mistake.” European officials have