It's reported this week that "Trump aides were in constant touch with senior Russian officials during [the presidential] campaign".
In the CNN article linked above, it states that it's not unusual for a campaign staff and representatives to communicate with foreign governments.
Officials emphasized that communications between campaign staff and representatives of foreign governments are not unusual. However, these communications stood out to investigators due to the frequency and the level of the Trump advisers involved. Investigators have not reached a judgment on the intent of those conversations.
So, is this unusual? Have there been precedents of other campaigns in the past that communicated with foreign governments during the election campaign?
Non-opinionated answers with sources are appreciated.