washington secretary state rex tillerson write leaders u.s. senate urge ratification montenegro new member nato alliance say strongly interest unite state letter date march see reuters tuesday tillerson argue montenegro membership alliance would support great integration democratic reform trade security stability among neighbor moscow oppose expansion north atlantic treaty organization delay u.s. approval montenegro accession fuel question whether president donald trump administration republican party stand russia despite trump desire good relations letter emerge amid flap new secretary state relationship alliance reuters report monday tillerson plan skip meet nato foreign minister next month order stay home visit china president plan visit russia late april tuesday administration reverse course propose new date meet set april brussels montenegro former yugoslav republic population 650,000 hop win require approval 28 nato ally time become full member summit may early month approve 24. nato members see montenegro accession way counter russia efforts expand influence balkans objections least two republican senators rand paul mike lee block quick vote full u.s. senate months senate leaders schedule time-consuming roll-call vote paul question wisdom anger russia take potential expense approve nato membership tiny country could play significant role defend unite state letter senate republican majority leader mitch mcconnell copy chuck schumer chamber top democrat tillerson say would immeasurably helpful senate schedule floor vote complete ratification procedures time trump participation may nato summit montenegro participation may nato summit full member observer send strong signal transatlantic unity tillerson add strongly interest unite state montenegro membership nato ratify write spokesman mcconnell say monday vote yet schedule montenegro nato membership already approve senate foreign relations committee paul senator john mccain one lead russia hawk u.s. congress heat exchange issue senate last week mccain say paul work russian president vladimir putin block quick vote montenegro paul call mccain unhinge past prime exclusive tillerson urge senate ratification montenegro 's nato membership